diff --git a/Zend/zend_compile.c b/Zend/zend_compile.c
index 039e95913f6d..94e458b420bf 100644
--- a/Zend/zend_compile.c
+++ b/Zend/zend_compile.c
@@ -1890,7 +1890,7 @@ ZEND_API size_t zend_dirname(char *path, size_t len)
 	/* Note that on Win32 CWD is per drive (heritage from CP/M).
 	 * This means dirname("c:foo") maps to "c:." or "c:" - which means CWD on C: drive.
 	 */
-	if ((2 <= len) && isalpha((int)((unsigned char *)path)[0]) && (':' == path[1])) {
+	if ((2 <= len) && zend_isalpha_ascii((int)((unsigned char *)path)[0]) && (':' == path[1])) {
 		/* Skip over the drive spec (if any) so as not to change */
 		path += 2;
 		len_adjust += 2;
diff --git a/Zend/zend_operators.c b/Zend/zend_operators.c
index de3664f5c653..6aa025360e43 100644
--- a/Zend/zend_operators.c
+++ b/Zend/zend_operators.c
@@ -118,9 +118,70 @@ ZEND_API const unsigned char zend_toupper_map[256] = {
 0xc0,0xc1,0xc2,0xc3,0xc4,0xc5,0xc6,0xc7,0xc8,0xc9,0xca,0xcb,0xcc,0xcd,0xce,0xcf,
 0xd0,0xd1,0xd2,0xd3,0xd4,0xd5,0xd6,0xd7,0xd8,0xd9,0xda,0xdb,0xdc,0xdd,0xde,0xdf,
 0xe0,0xe1,0xe2,0xe3,0xe4,0xe5,0xe6,0xe7,0xe8,0xe9,0xea,0xeb,0xec,0xed,0xee,0xef,
-0xf0,0xf1,0xf2,0xf3,0xf4,0xf5,0xf6,0xf7,0xf8,0xf9,0xfa,0xfb,0xfc,0xfd,0xfe,0xff	
+0xf0,0xf1,0xf2,0xf3,0xf4,0xf5,0xf6,0xf7,0xf8,0xf9,0xfa,0xfb,0xfc,0xfd,0xfe,0xff
+};
+
+/* ctype's isalpha varies based on locale, which is not what we want for many use cases.
+ * This is what it'd be in the "C" locale. */
+ZEND_API const bool zend_isalpha_map[256] = {
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
+1,1,1,1,1,1,1,1,1,1,1,0,0,0,0,0,
+0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
+1,1,1,1,1,1,1,1,1,1,1,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
 };
 
+/* ctype's isalnum is isalpha + isdigit(0-9) */
+ZEND_API const bool zend_isalnum_map[256] = {
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+1,1,1,1,1,1,1,1,1,1,0,0,0,0,0,0,
+0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
+1,1,1,1,1,1,1,1,1,1,1,0,0,0,0,0,
+0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
+1,1,1,1,1,1,1,1,1,1,1,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+};
+
+/* ctype's iscntrl varies based on locale, which is not what we want for many use cases.
+ * This is what it'd be in the "C" locale. */
+ZEND_API const bool zend_iscntrl_map[256] = {
+1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
+1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+};
 
 /**
  * Functions using locale lowercase:
diff --git a/Zend/zend_operators.h b/Zend/zend_operators.h
index eb88eedb79da..a22b5ba0b927 100644
--- a/Zend/zend_operators.h
+++ b/Zend/zend_operators.h
@@ -435,9 +435,15 @@ ZEND_API int ZEND_FASTCALL string_locale_compare_function(zval *op1, zval *op2);
 
 ZEND_API extern const unsigned char zend_tolower_map[256];
 ZEND_API extern const unsigned char zend_toupper_map[256];
+ZEND_API extern const bool zend_isalpha_map[256];
+ZEND_API extern const bool zend_isalnum_map[256];
+ZEND_API extern const bool zend_iscntrl_map[256];
 
 #define zend_tolower_ascii(c) (zend_tolower_map[(unsigned char)(c)])
 #define zend_toupper_ascii(c) (zend_toupper_map[(unsigned char)(c)])
+#define zend_isalpha_ascii(c) (zend_isalpha_map[(unsigned char)(c)])
+#define zend_isalnum_ascii(c) (zend_isalnum_map[(unsigned char)(c)])
+#define zend_iscntrl_ascii(c) (zend_iscntrl_map[(unsigned char)(c)])
 
 ZEND_API void         ZEND_FASTCALL zend_str_tolower(char *str, size_t length);
 ZEND_API void         ZEND_FASTCALL zend_str_toupper(char *str, size_t length);
diff --git a/Zend/zend_virtual_cwd.h b/Zend/zend_virtual_cwd.h
index 728e3ba69d88..c5407f0d660c 100644
--- a/Zend/zend_virtual_cwd.h
+++ b/Zend/zend_virtual_cwd.h
@@ -82,7 +82,7 @@ typedef unsigned short mode_t;
 #define IS_UNC_PATH(path, len) \
 	(len >= 2 && IS_SLASH(path[0]) && IS_SLASH(path[1]))
 #define IS_ABSOLUTE_PATH(path, len) \
-	(len >= 2 && (/* is local */isalpha(path[0]) && path[1] == ':' || /* is UNC */IS_SLASH(path[0]) && IS_SLASH(path[1])))
+	(len >= 2 && (/* is local */zend_isalpha_ascii(path[0]) && path[1] == ':' || /* is UNC */IS_SLASH(path[0]) && IS_SLASH(path[1])))
 
 #else
 #ifdef HAVE_DIRENT_H
diff --git a/ext/fileinfo/libmagic/apprentice.c b/ext/fileinfo/libmagic/apprentice.c
index 8cfdb5e19d9c..b5db9420b43f 100644
--- a/ext/fileinfo/libmagic/apprentice.c
+++ b/ext/fileinfo/libmagic/apprentice.c
@@ -299,7 +299,7 @@ get_standard_integer_type(const char *l, const char **t)
 {
 	int type;
 
-	if (isalpha(CAST(unsigned char, l[1]))) {
+	if (zend_isalpha_ascii(CAST(unsigned char, l[1]))) {
 		switch (l[1]) {
 		case 'C':
 			/* "dC" and "uC" */
@@ -1187,7 +1187,7 @@ load_1(struct magic_set *ms, int action, const char *fn, int *errs,
 					continue;
 				}
 				if ((*bang[i].fun)(ms, &me,
-				    line + bang[i].len + 2, 
+				    line + bang[i].len + 2,
 				    len - bang[i].len - 2) != 0) {
 					(*errs)++;
 					continue;
@@ -1419,7 +1419,7 @@ apprentice_load(struct magic_set *ms, const char *fn, int action)
 		/* coalesce per file arrays into a single one, if needed */
 		if (mset[j].count == 0)
 			continue;
-		      
+
 		if (coalesce_entries(ms, mset[j].me, mset[j].count,
 		    &map->magic[j], &map->nmagic[j]) == -1) {
 			errs++;
@@ -2071,7 +2071,7 @@ parse(struct magic_set *ms, struct magic_entry *me, const char *line,
 			if (*l == 'd')
 				m->type = get_standard_integer_type(l, &l);
 			else if (*l == 's'
-			    && !isalpha(CAST(unsigned char, l[1]))) {
+			    && !zend_isalpha_ascii(CAST(unsigned char, l[1]))) {
 				m->type = FILE_STRING;
 				++l;
 			}
@@ -2287,7 +2287,7 @@ parse_strength(struct magic_set *ms, struct magic_entry *me, const char *line,
 private int
 goodchar(unsigned char x, const char *extra)
 {
-	return (isascii(x) && isalnum(x)) || strchr(extra, x);
+	return (zend_isalnum_ascii(x)) || strchr(extra, x);
 }
 
 private int
diff --git a/ext/fileinfo/libmagic/compress.c b/ext/fileinfo/libmagic/compress.c
index 85d0b2938e49..4c4d94f0debd 100644
--- a/ext/fileinfo/libmagic/compress.c
+++ b/ext/fileinfo/libmagic/compress.c
@@ -237,7 +237,7 @@ format_decompression_error(struct magic_set *ms, size_t i, unsigned char *buf)
 		return file_printf(ms, "ERROR:[%s: %s]", methodname(i), buf);
 
 	for (p = buf; *p; p++)
-		if (!isalnum(*p))
+		if (!zend_isalnum_ascii(*p))
 			*p = '-';
 
 	return file_printf(ms, "application/x-decompression-error-%s-%s",
diff --git a/ext/fileinfo/libmagic/encoding.c b/ext/fileinfo/libmagic/encoding.c
index c0378f45c971..16c83a53bf65 100644
--- a/ext/fileinfo/libmagic/encoding.c
+++ b/ext/fileinfo/libmagic/encoding.c
@@ -536,7 +536,7 @@ looks_ucs32(const unsigned char *bf, size_t nbytes, file_unichar_t *ubf,
 			    | (CAST(file_unichar_t, bf[i]) << 24);
 		else
 			ubf[(*ulen)++] = CAST(file_unichar_t, bf[i + 0])
-			    | (CAST(file_unichar_t, bf[i + 1]) << 8) 
+			    | (CAST(file_unichar_t, bf[i + 1]) << 8)
 			    | (CAST(file_unichar_t, bf[i + 2]) << 16)
 			    | (CAST(file_unichar_t, bf[i + 3]) << 24);
 
diff --git a/ext/fileinfo/libmagic/funcs.c b/ext/fileinfo/libmagic/funcs.c
index b5e5731494ba..20009a8d007f 100644
--- a/ext/fileinfo/libmagic/funcs.c
+++ b/ext/fileinfo/libmagic/funcs.c
@@ -120,7 +120,7 @@ file_checkfmt(char *msg, size_t mlen, const char *fmt)
 				return -1;
 		}
 
-		if (!isalpha((unsigned char)*p)) {
+		if (!zend_isalpha_ascii((unsigned char)*p)) {
 			if (msg)
 				snprintf(msg, mlen, "bad format char: %c", *p);
 			return -1;
diff --git a/ext/filter/logical_filters.c b/ext/filter/logical_filters.c
index 108e8e3259c7..5641eaa16eae 100644
--- a/ext/filter/logical_filters.c
+++ b/ext/filter/logical_filters.c
@@ -528,21 +528,21 @@ static int _php_filter_validate_domain(char * domain, int len, zend_long flags)
 	}
 
 	/* First char must be alphanumeric */
-	if(*s == '.' || (hostname && !isalnum((int)*(unsigned char *)s))) {
+	if(*s == '.' || (hostname && !zend_isalnum_ascii((int)*(unsigned char *)s))) {
 		return 0;
 	}
 
 	while (s < e) {
 		if (*s == '.') {
 			/* The first and the last character of a label must be alphanumeric */
-			if (*(s + 1) == '.' || (hostname && (!isalnum((int)*(unsigned char *)(s - 1)) || !isalnum((int)*(unsigned char *)(s + 1))))) {
+			if (*(s + 1) == '.' || (hostname && (!zend_isalnum_ascii((int)*(unsigned char *)(s - 1)) || !zend_isalnum_ascii((int)*(unsigned char *)(s + 1))))) {
 				return 0;
 			}
 
 			/* Reset label length counter */
 			i = 1;
 		} else {
-			if (i > 63 || (hostname && *s != '-' && !isalnum((int)*(unsigned char *)s))) {
+			if (i > 63 || (hostname && *s != '-' && !zend_isalnum_ascii((int)*(unsigned char *)s))) {
 				return 0;
 			}
 
@@ -569,7 +569,7 @@ static int is_userinfo_valid(zend_string *str)
 	const char *valid = "-._~!$&'()*+,;=:";
 	const char *p = ZSTR_VAL(str);
 	while (p - ZSTR_VAL(str) < ZSTR_LEN(str)) {
-		if (isalpha(*p) || isdigit(*p) || strchr(valid, *p)) {
+		if (zend_isalnum_ascii(*p) || strchr(valid, *p)) {
 			p++;
 		} else if (*p == '%' && p - ZSTR_VAL(str) <= ZSTR_LEN(str) - 3 && isdigit(*(p+1)) && isxdigit(*(p+2))) {
 			p += 3;
diff --git a/ext/filter/tests/filter_validate_domain_locale.phpt b/ext/filter/tests/filter_validate_domain_locale.phpt
new file mode 100644
index 000000000000..2e8ad014491e
--- /dev/null
+++ b/ext/filter/tests/filter_validate_domain_locale.phpt
@@ -0,0 +1,19 @@
+--TEST--
+FILTER_VALIDATE_DOMAIN FILTER_FLAG_HOSTNAME should not be locale dependent
+--EXTENSIONS--
+filter
+--SKIPIF--
+<?php  // try to activate a single-byte german locale
+if (!setlocale(LC_ALL, "de_DE")) {
+    print "skip Can't find german locale";
+}
+?>
+--FILE--
+<?php
+var_dump(filter_var('٪', FILTER_VALIDATE_DOMAIN, FILTER_FLAG_HOSTNAME));
+setlocale(LC_ALL, "de_DE");
+var_dump(filter_var('٪', FILTER_VALIDATE_DOMAIN, FILTER_FLAG_HOSTNAME));
+?>
+--EXPECT--
+bool(false)
+bool(false)
diff --git a/ext/gd/libgd/gd_xbm.c b/ext/gd/libgd/gd_xbm.c
index 3c655a2998c1..ff76b414a4a4 100644
--- a/ext/gd/libgd/gd_xbm.c
+++ b/ext/gd/libgd/gd_xbm.c
@@ -190,8 +190,8 @@ void gdImageXbmCtx(gdImagePtr image, char* file_name, int fg, gdIOCtx * out)
 		name = estrdup("image");
 	} else {
 		for (i=0; i<l; i++) {
-			/* only in C-locale isalnum() would work */
-			if (!isupper(name[i]) && !islower(name[i]) && !isdigit(name[i])) {
+			/* Locale-independent check */
+			if (!zend_isalnum_ascii(name[i])) {
 				name[i] = '_';
 			}
 		}
diff --git a/ext/imap/php_imap.c b/ext/imap/php_imap.c
index b6d2dd8b74da..0b3762fc78a5 100644
--- a/ext/imap/php_imap.c
+++ b/ext/imap/php_imap.c
@@ -2306,7 +2306,7 @@ PHP_FUNCTION(imap_utf8)
 #define SPECIAL(c) ((c) <= 0x1f || (c) >= 0x7f)
 
 /* validate a modified-base64 character */
-#define B64CHAR(c) (isalnum(c) || (c) == '+' || (c) == ',')
+#define B64CHAR(c) (zend_isalnum_ascii(c) || (c) == '+' || (c) == ',')
 
 /* map the low 64 bits of `n' to the modified-base64 characters */
 #define B64(n)	("ABCDEFGHIJKLMNOPQRSTUVWXYZ" \
diff --git a/ext/mbstring/mbstring.c b/ext/mbstring/mbstring.c
index bcf2ee51933d..6a9e39efd21f 100644
--- a/ext/mbstring/mbstring.c
+++ b/ext/mbstring/mbstring.c
@@ -3622,7 +3622,7 @@ PHP_FUNCTION(mb_send_mail)
 			to_r[to_len - 1] = '\0';
 		}
 		for (i = 0; to_r[i]; i++) {
-			if (iscntrl((unsigned char) to_r[i])) {
+			if (zend_iscntrl_ascii((unsigned char) to_r[i])) {
 				/* According to RFC 822, section 3.1.1 long headers may be separated into
 				 * parts using CRLF followed at least one linear-white-space character ('\t' or ' ').
 				 * To prevent these separators from being replaced with a space, we skip over them. */
diff --git a/ext/standard/file.c b/ext/standard/file.c
index 4c31ee0eae66..986c6a72ba53 100644
--- a/ext/standard/file.c
+++ b/ext/standard/file.c
@@ -2405,10 +2405,10 @@ php_meta_tags_token php_next_meta_token(php_meta_tags_data *md)
 				break;
 
 			default:
-				if (isalnum(ch)) {
+				if (zend_isalnum_ascii(ch)) {
 					md->token_len = 0;
 					buff[(md->token_len)++] = ch;
-					while (!php_stream_eof(md->stream) && (ch = php_stream_getc(md->stream)) && (isalnum(ch) || strchr(PHP_META_HTML401_CHARS, ch))) {
+					while (!php_stream_eof(md->stream) && (ch = php_stream_getc(md->stream)) && (zend_isalnum_ascii(ch) || strchr(PHP_META_HTML401_CHARS, ch))) {
 						buff[(md->token_len)++] = ch;
 
 						if (md->token_len == META_DEF_BUFSIZE) {
@@ -2417,7 +2417,7 @@ php_meta_tags_token php_next_meta_token(php_meta_tags_data *md)
 					}
 
 					/* This is ugly, but we have to replace ungetc */
-					if (!isalpha(ch) && ch != '-') {
+					if (!zend_isalnum_ascii(ch) && ch != '-') {
 						md->ulc = 1;
 						md->lc = ch;
 					}
diff --git a/ext/standard/formatted_print.c b/ext/standard/formatted_print.c
index b988422df21c..24dc89746589 100644
--- a/ext/standard/formatted_print.c
+++ b/ext/standard/formatted_print.c
@@ -466,7 +466,7 @@ php_formatted_print(char *format, size_t format_len, zval *args, int argc, int n
 
 			PRINTF_DEBUG(("sprintf: first looking at '%c', inpos=%d\n",
 						  *format, format - Z_STRVAL_P(z_format)));
-			if (isalpha((int)*format)) {
+			if (zend_isalpha_ascii((int)*format)) {
 				width = precision = 0;
 				argnum = ARG_NUM_NEXT;
 			} else {
diff --git a/ext/standard/ftp_fopen_wrapper.c b/ext/standard/ftp_fopen_wrapper.c
index f20f4245bd46..5a1fdce80f98 100644
--- a/ext/standard/ftp_fopen_wrapper.c
+++ b/ext/standard/ftp_fopen_wrapper.c
@@ -228,7 +228,7 @@ static php_stream *php_ftp_fopen_connect(php_stream_wrapper *wrapper, const char
 #define PHP_FTP_CNTRL_CHK(val, val_len, err_msg) {	\
 	unsigned char *s = (unsigned char *) val, *e = (unsigned char *) s + val_len;	\
 	while (s < e) {	\
-		if (iscntrl(*s)) {	\
+		if (zend_iscntrl_ascii(*s)) {	\
 			php_stream_wrapper_log_error(wrapper, options, err_msg, val);	\
 			goto connect_errexit;	\
 		}	\
diff --git a/ext/standard/http_fopen_wrapper.c b/ext/standard/http_fopen_wrapper.c
index b5132d9e005a..83daa84504d5 100644
--- a/ext/standard/http_fopen_wrapper.c
+++ b/ext/standard/http_fopen_wrapper.c
@@ -895,7 +895,7 @@ static php_stream *php_stream_url_wrap_http_ex(php_stream_wrapper *wrapper,
 		ZSTR_LEN(val) = php_url_decode(ZSTR_VAL(val), ZSTR_LEN(val)); \
 		s = (unsigned char*)ZSTR_VAL(val); e = s + ZSTR_LEN(val); \
 		while (s < e) { \
-			if (iscntrl(*s)) { \
+			if (zend_iscntrl_ascii(*s)) { \
 				php_stream_wrapper_log_error(wrapper, options, "Invalid redirect URL! %s", new_path); \
 				goto out; \
 			} \
diff --git a/ext/standard/mail.c b/ext/standard/mail.c
index bc5a06bec9cc..e3c3b78ebf9b 100644
--- a/ext/standard/mail.c
+++ b/ext/standard/mail.c
@@ -242,7 +242,7 @@ PHP_FUNCTION(mail)
 			to_r[to_len - 1] = '\0';
 		}
 		for (i = 0; to_r[i]; i++) {
-			if (iscntrl((unsigned char) to_r[i])) {
+			if (zend_iscntrl_ascii((unsigned char) to_r[i])) {
 				/* According to RFC 822, section 3.1.1 long headers may be separated into
 				 * parts using CRLF followed at least one linear-white-space character ('\t' or ' ').
 				 * To prevent these separators from being replaced with a space, we use the
@@ -264,7 +264,7 @@ PHP_FUNCTION(mail)
 			subject_r[subject_len - 1] = '\0';
 		}
 		for (i = 0; subject_r[i]; i++) {
-			if (iscntrl((unsigned char) subject_r[i])) {
+			if (zend_iscntrl_ascii((unsigned char) subject_r[i])) {
 				SKIP_LONG_HEADER_SEP(subject_r, i);
 				subject_r[i] = ' ';
 			}
diff --git a/ext/standard/metaphone.c b/ext/standard/metaphone.c
index 2ba7a839c88e..45120484dd3d 100644
--- a/ext/standard/metaphone.c
+++ b/ext/standard/metaphone.c
@@ -77,8 +77,8 @@ static const char _codes[26] =
 /*  a  b c  d e f g  h i j k l m n o p q r s t u v w x y z */
 };
 
-
-#define ENCODE(c) (isalpha(c) ? _codes[((toupper(c)) - 'A')] : 0)
+/* Here, this avoids locale dependency to ensure the index is a valid index of _codes. */
+#define ENCODE(c) (zend_isalpha_ascii(c) ? _codes[((zend_toupper_ascii(c)) - 'A')] : 0)
 
 #define isvowel(c)  (ENCODE(c) & 1)		/* AEIOU */
 
diff --git a/ext/standard/quot_print.c b/ext/standard/quot_print.c
index e6aa2e43f4c6..898a042c9943 100644
--- a/ext/standard/quot_print.c
+++ b/ext/standard/quot_print.c
@@ -158,7 +158,7 @@ PHPAPI zend_string *php_quot_print_encode(const unsigned char *str, size_t lengt
 			length--;
 			lp = 0;
 		} else {
-			if (iscntrl (c) || (c == 0x7f) || (c & 0x80) || (c == '=') || ((c == ' ') && (*str == '\015'))) {
+			if (zend_iscntrl_ascii(c) || (c == 0x7f) || (c & 0x80) || (c == '=') || ((c == ' ') && (*str == '\015'))) {
 				if ((((lp+= 3) > PHP_QPRINT_MAXL) && (c <= 0x7f))
 				    || ((c > 0x7f) && (c <= 0xdf) && ((lp + 3) > PHP_QPRINT_MAXL))
 				    || ((c > 0xdf) && (c <= 0xef) && ((lp + 6) > PHP_QPRINT_MAXL))
diff --git a/ext/standard/tests/streams/locale.phpt b/ext/standard/tests/streams/locale.phpt
new file mode 100644
index 000000000000..5f09b2d595fb
--- /dev/null
+++ b/ext/standard/tests/streams/locale.phpt
@@ -0,0 +1,28 @@
+--TEST--
+Stream wrappers should not be locale dependent
+--SKIPIF--
+<?php  // try to activate a single-byte german locale
+if (!setlocale(LC_ALL, "de_DE")) {
+    print "skip Can't find german locale";
+}
+?>
+--INI--
+allow_url_fopen=1
+display_errors=stderr
+--FILE--
+<?php
+setlocale(LC_ALL, "de_DE");
+class testwrapper {
+}
+
+var_dump(ctype_alpha('٪'));  // \xd9 and \xaa are both alphabetical in the german locale
+var_dump(stream_wrapper_register("test٪", 'testwrapper', STREAM_IS_URL));
+
+echo 'stream_open: ';
+fopen("test٪://test", 'r');
+?>
+--EXPECTF--
+bool(true)
+Warning: stream_wrapper_register(): Invalid protocol scheme specified. Unable to register wrapper class testwrapper to test٪:// in %s on line 7
+bool(false)
+stream_open: Warning: fopen(test٪://test): Failed to open stream: No such file or directory in %s on line 10
diff --git a/ext/standard/tests/url/parse_url_locale.phpt b/ext/standard/tests/url/parse_url_locale.phpt
new file mode 100644
index 000000000000..5102ee8f3225
--- /dev/null
+++ b/ext/standard/tests/url/parse_url_locale.phpt
@@ -0,0 +1,21 @@
+--TEST--
+Bug #52923 (Locale settings affecting parse_url)
+--SKIPIF--
+<?php  // try to activate a german locale
+if (!setlocale(LC_ALL, "de_DE")) {
+    print "skip Can't find german locale";
+}
+?>
+--FILE--
+<?php
+echo http_build_query(parse_url("http\xfc://invalid"), true), "\n";
+// activate the german locale. With this bug fix, locale settings should no longer affect parse_url
+var_dump(setlocale(LC_CTYPE, "de_DE"));
+echo http_build_query(parse_url("http\xfc://invalid"), true), "\n";
+echo http_build_query(parse_url('http://mydomain.com/path/道')), "\n";
+?>
+--EXPECT--
+path=http%FC%3A%2F%2Finvalid
+string(5) "de_DE"
+path=http%FC%3A%2F%2Finvalid
+scheme=http&host=mydomain.com&path=%2Fpath%2F%E9%81%93
diff --git a/ext/standard/url.c b/ext/standard/url.c
index e3d95768fb01..2127da5eb311 100644
--- a/ext/standard/url.c
+++ b/ext/standard/url.c
@@ -61,7 +61,7 @@ PHPAPI char *php_replace_controlchars_ex(char *str, size_t len)
 
 	while (s < e) {
 
-		if (iscntrl(*s)) {
+		if (zend_iscntrl_ascii(*s)) {
 			*s='_';
 		}
 		s++;
@@ -117,7 +117,7 @@ PHPAPI php_url *php_url_parse_ex2(char const *str, size_t length, bool *has_port
 		p = s;
 		while (p < e) {
 			/* scheme = 1*[ lowalpha | digit | "+" | "-" | "." ] */
-			if (!isalpha(*p) && !isdigit(*p) && *p != '+' && *p != '.' && *p != '-') {
+			if (!zend_isalnum_ascii(*p) && *p != '+' && *p != '.' && *p != '-') {
 				if (e + 1 < ue && e < binary_strcspn(s, ue, "?#")) {
 					goto parse_port;
 				} else if (s + 1 < ue && *s == '/' && *(s + 1) == '/') { /* relative-scheme URL */
diff --git a/ext/standard/versioning.c b/ext/standard/versioning.c
index aa60d9746722..58dd57dc174a 100644
--- a/ext/standard/versioning.c
+++ b/ext/standard/versioning.c
@@ -59,7 +59,7 @@ php_canonicalize_version(const char *version)
 				*q++ = '.';
 			}
 			*q++ = *p;
-		} else if (!isalnum(*p)) {
+		} else if (!zend_isalnum_ascii(*p)) {
 			if (lq != '.') {
 				*q++ = '.';
 			}
diff --git a/main/fopen_wrappers.c b/main/fopen_wrappers.c
index f6ce26e104be..0925771a5d23 100644
--- a/main/fopen_wrappers.c
+++ b/main/fopen_wrappers.c
@@ -485,7 +485,7 @@ PHPAPI zend_string *php_resolve_path(const char *filename, size_t filename_lengt
 	}
 
 	/* Don't resolve paths which contain protocol (except of file://) */
-	for (p = filename; isalnum((int)*p) || *p == '+' || *p == '-' || *p == '.'; p++);
+	for (p = filename; zend_isalnum_ascii((int)*p) || *p == '+' || *p == '-' || *p == '.'; p++);
 	if ((*p == ':') && (p - filename > 1) && (p[1] == '/') && (p[2] == '/')) {
 		wrapper = php_stream_locate_url_wrapper(filename, &actual_path, STREAM_OPEN_FOR_INCLUDE);
 		if (wrapper == &php_plain_files_wrapper) {
@@ -517,7 +517,7 @@ PHPAPI zend_string *php_resolve_path(const char *filename, size_t filename_lengt
 		/* Check for stream wrapper */
 		int is_stream_wrapper = 0;
 
-		for (p = ptr; isalnum((int)*p) || *p == '+' || *p == '-' || *p == '.'; p++);
+		for (p = ptr; zend_isalnum_ascii((int)*p) || *p == '+' || *p == '-' || *p == '.'; p++);
 		if ((*p == ':') && (p - ptr > 1) && (p[1] == '/') && (p[2] == '/')) {
 			/* .:// or ..:// is not a stream wrapper */
 			if (p[-1] != '.' || p[-2] != '.' || p - 2 != ptr) {
@@ -586,7 +586,7 @@ PHPAPI zend_string *php_resolve_path(const char *filename, size_t filename_lengt
 			actual_path = trypath;
 
 			/* Check for stream wrapper */
-			for (p = trypath; isalnum((int)*p) || *p == '+' || *p == '-' || *p == '.'; p++);
+			for (p = trypath; zend_isalnum_ascii((int)*p) || *p == '+' || *p == '-' || *p == '.'; p++);
 			if ((*p == ':') && (p - trypath > 1) && (p[1] == '/') && (p[2] == '/')) {
 				wrapper = php_stream_locate_url_wrapper(trypath, &actual_path, STREAM_OPEN_FOR_INCLUDE);
 				if (!wrapper) {
diff --git a/main/snprintf.c b/main/snprintf.c
index 3c379c5c2ce1..e499640a7ddc 100644
--- a/main/snprintf.c
+++ b/main/snprintf.c
@@ -288,7 +288,7 @@ PHPAPI char * php_conv_fp(char format, double num,
 	/*
 	 * Check for Infinity and NaN
 	 */
-	if (isalpha((int)*p)) {
+	if (zend_isalpha_ascii((int)*p)) {
 		*len = strlen(p);
 		memcpy(buf, p, *len + 1);
 		*is_negative = false;
diff --git a/main/streams/streams.c b/main/streams/streams.c
index 8a7e32800721..eb282da81dee 100644
--- a/main/streams/streams.c
+++ b/main/streams/streams.c
@@ -1734,7 +1734,7 @@ static inline zend_result php_stream_wrapper_scheme_validate(const char *protoco
 	unsigned int i;
 
 	for(i = 0; i < protocol_len; i++) {
-		if (!isalnum((int)protocol[i]) &&
+		if (!zend_isalnum_ascii((int)protocol[i]) &&
 			protocol[i] != '+' &&
 			protocol[i] != '-' &&
 			protocol[i] != '.') {
@@ -1814,7 +1814,7 @@ PHPAPI php_stream_wrapper *php_stream_locate_url_wrapper(const char *path, const
 		return (php_stream_wrapper*)((options & STREAM_LOCATE_WRAPPERS_ONLY) ? NULL : &php_plain_files_wrapper);
 	}
 
-	for (p = path; isalnum((int)*p) || *p == '+' || *p == '-' || *p == '.'; p++) {
+	for (p = path; zend_isalnum_ascii((int)*p) || *p == '+' || *p == '-' || *p == '.'; p++) {
 		n++;
 	}
 
diff --git a/main/streams/transports.c b/main/streams/transports.c
index de6b968868ed..79ef03f60435 100644
--- a/main/streams/transports.c
+++ b/main/streams/transports.c
@@ -93,7 +93,7 @@ PHPAPI php_stream *_php_stream_xport_create(const char *name, size_t namelen, in
 		}
 	}
 
-	for (p = name; isalnum((int)*p) || *p == '+' || *p == '-' || *p == '.'; p++) {
+	for (p = name; zend_isalnum_ascii((int)*p) || *p == '+' || *p == '-' || *p == '.'; p++) {
 		n++;
 	}
 
diff --git a/sapi/cgi/cgi_main.c b/sapi/cgi/cgi_main.c
index 75511ef3bd70..1cb7b1da934c 100644
--- a/sapi/cgi/cgi_main.c
+++ b/sapi/cgi/cgi_main.c
@@ -1830,7 +1830,7 @@ int main(int argc, char *argv[])
 
 				if ((val = strchr(php_optarg, '='))) {
 					val++;
-					if (!isalnum(*val) && *val != '"' && *val != '\'' && *val != '\0') {
+					if (!zend_isalnum_ascii(*val) && *val != '"' && *val != '\'' && *val != '\0') {
 						cgi_sapi_module.ini_entries = realloc(cgi_sapi_module.ini_entries, ini_entries_len + len + sizeof("\"\"\n\0"));
 						memcpy(cgi_sapi_module.ini_entries + ini_entries_len, php_optarg, (val - php_optarg));
 						ini_entries_len += (val - php_optarg);
diff --git a/sapi/cli/php_cli.c b/sapi/cli/php_cli.c
index fdd604cec53b..044036c586ca 100644
--- a/sapi/cli/php_cli.c
+++ b/sapi/cli/php_cli.c
@@ -1257,7 +1257,7 @@ int main(int argc, char *argv[])
 
 				if ((val = strchr(php_optarg, '='))) {
 					val++;
-					if (!isalnum(*val) && *val != '"' && *val != '\'' && *val != '\0') {
+					if (!zend_isalnum_ascii(*val) && *val != '"' && *val != '\'' && *val != '\0') {
 						ini_entries = realloc(ini_entries, ini_entries_len + len + sizeof("\"\"\n\0"));
 						memcpy(ini_entries + ini_entries_len, php_optarg, (val - php_optarg));
 						ini_entries_len += (val - php_optarg);
diff --git a/sapi/fpm/fpm/fpm_conf.c b/sapi/fpm/fpm/fpm_conf.c
index 0464a36f1680..a023a02627f2 100644
--- a/sapi/fpm/fpm/fpm_conf.c
+++ b/sapi/fpm/fpm/fpm_conf.c
@@ -933,7 +933,7 @@ static int fpm_conf_process_all_pools(void) /* {{{ */
 			}
 
 			for (i = 0; i < strlen(status); i++) {
-				if (!isalnum(status[i]) && status[i] != '/' && status[i] != '-' && status[i] != '_' && status[i] != '.' && status[i] != '~') {
+				if (!zend_isalnum_ascii(status[i]) && status[i] != '/' && status[i] != '-' && status[i] != '_' && status[i] != '.' && status[i] != '~') {
 					zlog(ZLOG_ERROR, "[pool %s] the status path '%s' must contain only the following characters '[alphanum]/_-.~'", wp->config->name, status);
 					return -1;
 				}
@@ -956,7 +956,7 @@ static int fpm_conf_process_all_pools(void) /* {{{ */
 			}
 
 			for (i = 0; i < strlen(ping); i++) {
-				if (!isalnum(ping[i]) && ping[i] != '/' && ping[i] != '-' && ping[i] != '_' && ping[i] != '.' && ping[i] != '~') {
+				if (!zend_isalnum_ascii(ping[i]) && ping[i] != '/' && ping[i] != '-' && ping[i] != '_' && ping[i] != '.' && ping[i] != '~') {
 					zlog(ZLOG_ERROR, "[pool %s] the ping path '%s' must contain only the following characters '[alphanum]/_-.~'", wp->config->name, ping);
 					return -1;
 				}
diff --git a/sapi/fpm/fpm/fpm_main.c b/sapi/fpm/fpm/fpm_main.c
index 657ff72b673a..e581191f9696 100644
--- a/sapi/fpm/fpm/fpm_main.c
+++ b/sapi/fpm/fpm/fpm_main.c
@@ -1587,7 +1587,7 @@ int main(int argc, char *argv[])
 
 				if ((val = strchr(php_optarg, '='))) {
 					val++;
-					if (!isalnum(*val) && *val != '"' && *val != '\'' && *val != '\0') {
+					if (!zend_isalnum_ascii(*val) && *val != '"' && *val != '\'' && *val != '\0') {
 						cgi_sapi_module.ini_entries = realloc(cgi_sapi_module.ini_entries, ini_entries_len + len + sizeof("\"\"\n\0"));
 						memcpy(cgi_sapi_module.ini_entries + ini_entries_len, php_optarg, (val - php_optarg));
 						ini_entries_len += (val - php_optarg);
diff --git a/sapi/phpdbg/phpdbg.c b/sapi/phpdbg/phpdbg.c
index 42a2a9c03643..61ab9323f15c 100644
--- a/sapi/phpdbg/phpdbg.c
+++ b/sapi/phpdbg/phpdbg.c
@@ -1216,7 +1216,7 @@ int main(int argc, char **argv) /* {{{ */
 
 				if ((val = strchr(php_optarg, '='))) {
 				  val++;
-				  if (!isalnum(*val) && *val != '"' && *val != '\'' && *val != '\0') {
+				  if (!zend_isalnum_ascii(*val) && *val != '"' && *val != '\'' && *val != '\0') {
 					  ini_entries = realloc(ini_entries, ini_entries_len + len + sizeof("\"\"\n\0"));
 					  memcpy(ini_entries + ini_entries_len, php_optarg, (val - php_optarg));
 					  ini_entries_len += (val - php_optarg);