diff --git a/ext/readline/readline_cli.c b/ext/readline/readline_cli.c
index 7a0fe78595e5b..8bf5d23df75f7 100644
--- a/ext/readline/readline_cli.c
+++ b/ext/readline/readline_cli.c
@@ -135,6 +135,7 @@ static zend_string *cli_get_prompt(char *block, char prompt) /* {{{ */
 {
 	smart_str retval = {0};
 	char *prompt_spec = CLIR_G(prompt) ? CLIR_G(prompt) : DEFAULT_PROMPT;
+	bool unicode_warned = false;
 
 	do {
 		if (*prompt_spec == '\\') {
@@ -193,7 +194,16 @@ static zend_string *cli_get_prompt(char *block, char prompt) /* {{{ */
 				prompt_spec = prompt_end;
 			}
 		} else {
-			smart_str_appendc(&retval, *prompt_spec);
+			if (!(*prompt_spec & 0x80)) {
+				smart_str_appendc(&retval, *prompt_spec);
+			} else {
+				if (!unicode_warned) {
+					zend_error(E_WARNING,
+						"prompt contains unsupported unicode characters");
+					unicode_warned = true;
+				}
+				smart_str_appendc(&retval, '?');
+			}
 		}
 	} while (++prompt_spec && *prompt_spec);
 	smart_str_0(&retval);
diff --git a/sapi/phpdbg/phpdbg_utils.c b/sapi/phpdbg/phpdbg_utils.c
index 272715654ebf2..0e46936fc627e 100644
--- a/sapi/phpdbg/phpdbg_utils.c
+++ b/sapi/phpdbg/phpdbg_utils.c
@@ -300,6 +300,23 @@ PHPDBG_API const char *phpdbg_get_prompt(void) /* {{{ */
 		return PHPDBG_G(prompt)[1];
 	}
 
+	uint32_t pos = 0,
+			 end = strlen(PHPDBG_G(prompt)[0]);
+	bool unicode_warned = false;
+
+	while (pos < end) {
+		if (PHPDBG_G(prompt)[0][pos] & 0x80) {
+			PHPDBG_G(prompt)[0][pos] = '?';
+
+			if (!unicode_warned) {
+				zend_error(E_WARNING,
+					"prompt contains unsupported unicode characters");
+				unicode_warned = true;
+			}
+		}
+		pos++;
+	}
+
 	/* create cached prompt */
 #ifndef HAVE_LIBEDIT
 	/* TODO: libedit doesn't seems to support coloured prompt */