diff --git a/ext/posix/posix.c b/ext/posix/posix.c
index bfb542bad7539..4ba3588a63a1b 100644
--- a/ext/posix/posix.c
+++ b/ext/posix/posix.c
@@ -426,10 +426,15 @@ static int php_posix_stream_get_fd(zval *zfp, zend_long *fd) /* {{{ */
 	if (stream == NULL) {
 		return 0;
 	}
-	if (php_stream_can_cast(stream, PHP_STREAM_AS_FD_FOR_SELECT) == SUCCESS) {
-		php_stream_cast(stream, PHP_STREAM_AS_FD_FOR_SELECT, (void*)fd, 0);
-	} else if (php_stream_can_cast(stream, PHP_STREAM_AS_FD) == SUCCESS) {
-		php_stream_cast(stream, PHP_STREAM_AS_FD, (void*)fd, 0);
+
+	/* get the fd.
+	 * NB: Most other code will NOT use the PHP_STREAM_CAST_INTERNAL flag when casting.
+	 * It is only used here so that the buffered data warning is not displayed.
+	 */
+	if (php_stream_can_cast(stream, PHP_STREAM_AS_FD_FOR_SELECT | PHP_STREAM_CAST_INTERNAL) == SUCCESS) {
+		php_stream_cast(stream, PHP_STREAM_AS_FD_FOR_SELECT | PHP_STREAM_CAST_INTERNAL, (void*)&fd, 0);
+	} else if (php_stream_can_cast(stream, PHP_STREAM_AS_FD | PHP_STREAM_CAST_INTERNAL) == SUCCESS) {
+		php_stream_cast(stream, PHP_STREAM_AS_FD | PHP_STREAM_CAST_INTERNAL, (void*)&fd, 0);
 	} else {
 		php_error_docref(NULL, E_WARNING, "Could not use stream of type '%s'",
 				stream->ops->label);
diff --git a/ext/posix/tests/posix_fpathconf.phpt b/ext/posix/tests/posix_fpathconf.phpt
index cc388d5c0971f..c114094160116 100644
--- a/ext/posix/tests/posix_fpathconf.phpt
+++ b/ext/posix/tests/posix_fpathconf.phpt
@@ -15,7 +15,7 @@ try {
 } catch (\TypeError $e) {
 	echo $e->getMessage() . "\n";
 }
-$fd = fopen(sys_get_temp_dir(), "r");
+$fd = fopen(__DIR__, "r");
 var_dump(posix_fpathconf($fd, POSIX_PC_PATH_MAX));
 fclose($fd);
 ?>
diff --git a/ext/posix/tests/posix_isatty.phpt b/ext/posix/tests/posix_isatty.phpt
index 5132c04d35ee9..b913a53c3e91a 100644
--- a/ext/posix/tests/posix_isatty.phpt
+++ b/ext/posix/tests/posix_isatty.phpt
@@ -2,15 +2,11 @@
 posix_isatty(): Basic tests
 --EXTENSIONS--
 posix
---SKIPIF--
-<?php
-if (!function_exists('posix_isatty')) die('skip posix_isatty() not found');
-?>
 --FILE--
 <?php
 
-var_dump(posix_isatty(0));
+var_dump(posix_isatty(STDIN));
 
 ?>
---EXPECTF--
-bool(%s)
+--EXPECT--
+bool(false)
diff --git a/ext/posix/tests/posix_isatty_no_warning_on_stream_cast.phpt b/ext/posix/tests/posix_isatty_no_warning_on_stream_cast.phpt
new file mode 100644
index 0000000000000..d49ac4bdf274c
--- /dev/null
+++ b/ext/posix/tests/posix_isatty_no_warning_on_stream_cast.phpt
@@ -0,0 +1,33 @@
+--TEST--
+posix_isatty(): casting stream does not emit data loss and should not emit warnings
+--EXTENSIONS--
+posix
+--SKIPIF--
+<?php
+require __DIR__ . '/../../standard/tests/http/server.inc'; http_server_skipif();
+?>
+--INI--
+allow_url_fopen=1
+--FILE--
+<?php
+
+require __DIR__ . '/../../standard/tests/http/server.inc';
+
+$responses = array(
+    "data://text/plain,HTTP/1.0 200 Ok\r\nSome: Header\r\nSome: Header\r\n\r\nBody",
+);
+
+['pid' => $pid, 'uri' => $uri] = http_server($responses, $output);
+
+/* Note: the warning is bogus in this case as no data actually gets lost,
+ * but this checks that stream casting works */
+$handle = fopen($uri, 'r');
+var_dump(posix_isatty($handle));
+var_dump(fread($handle, 20));
+fclose($handle);
+
+http_server_kill($pid);
+?>
+--EXPECT--
+bool(false)
+string(4) "Body"
diff --git a/ext/posix/tests/posix_isatty_non_castable_user_stream.phpt b/ext/posix/tests/posix_isatty_non_castable_user_stream.phpt
new file mode 100644
index 0000000000000..422e2c6fe4bb7
--- /dev/null
+++ b/ext/posix/tests/posix_isatty_non_castable_user_stream.phpt
@@ -0,0 +1,20 @@
+--TEST--
+posix_isatty(): uncastable user stream
+--EXTENSIONS--
+posix
+--FILE--
+<?php
+
+require dirname(__DIR__, 3) . '/tests/output/DummyStreamWrapper.inc';
+stream_wrapper_register('custom', DummyStreamWrapper::class);
+
+$fp = fopen("custom://myvar", "r+");
+var_dump(posix_isatty($fp));
+fclose($fp);
+
+echo "Done";
+?>
+--EXPECTF--
+Warning: posix_isatty(): Could not use stream of type 'user-space' in %s on line %d
+bool(false)
+Done
diff --git a/ext/posix/tests/posix_ttyname_no_warning_on_cast.phpt b/ext/posix/tests/posix_ttyname_no_warning_on_cast.phpt
new file mode 100644
index 0000000000000..596826c252588
--- /dev/null
+++ b/ext/posix/tests/posix_ttyname_no_warning_on_cast.phpt
@@ -0,0 +1,33 @@
+--TEST--
+posix_ttyname(): casting stream does not emit data loss and should not emit warnings
+--EXTENSIONS--
+posix
+--SKIPIF--
+<?php
+require __DIR__ . '/../../standard/tests/http/server.inc'; http_server_skipif();
+?>
+--INI--
+allow_url_fopen=1
+--FILE--
+<?php
+
+require __DIR__ . '/../../standard/tests/http/server.inc';
+
+$responses = array(
+    "data://text/plain,HTTP/1.0 200 Ok\r\nSome: Header\r\nSome: Header\r\n\r\nBody",
+);
+
+['pid' => $pid, 'uri' => $uri] = http_server($responses, $output);
+
+/* Note: the warning is bogus in this case as no data actually gets lost,
+ * but this checks that stream casting works */
+$handle = fopen($uri, 'r');
+var_dump(posix_ttyname($handle));
+var_dump(fread($handle, 20));
+fclose($handle);
+
+http_server_kill($pid);
+?>
+--EXPECT--
+bool(false)
+string(4) "Body"
diff --git a/ext/posix/tests/posix_ttyname_non_castable_user_stream.phpt b/ext/posix/tests/posix_ttyname_non_castable_user_stream.phpt
new file mode 100644
index 0000000000000..df81c0af0303c
--- /dev/null
+++ b/ext/posix/tests/posix_ttyname_non_castable_user_stream.phpt
@@ -0,0 +1,20 @@
+--TEST--
+posix_ttyname(): uncastable user stream
+--EXTENSIONS--
+posix
+--FILE--
+<?php
+
+require dirname(__DIR__, 3) . '/tests/output/DummyStreamWrapper.inc';
+stream_wrapper_register('custom', DummyStreamWrapper::class);
+
+$fp = fopen("custom://myvar", "r+");
+var_dump(posix_ttyname($fp));
+fclose($fp);
+
+echo "Done";
+?>
+--EXPECTF--
+Warning: posix_ttyname(): Could not use stream of type 'user-space' in %s on line %d
+bool(false)
+Done
diff --git a/ext/standard/streamsfuncs.c b/ext/standard/streamsfuncs.c
index 53fa8d33dad6b..5cb91959e2acf 100644
--- a/ext/standard/streamsfuncs.c
+++ b/ext/standard/streamsfuncs.c
@@ -74,14 +74,14 @@ PHP_FUNCTION(stream_socket_pair)
         close(pair[0]);
         close(pair[1]);
         php_error_docref(NULL, E_WARNING, "Failed to open stream from socketpair");
-        RETURN_FALSE;        
+        RETURN_FALSE;
     }
     s2 = php_stream_sock_open_from_socket(pair[1], 0);
     if (s2 == NULL) {
         php_stream_free(s1, PHP_STREAM_FREE_CLOSE);
         close(pair[1]);
         php_error_docref(NULL, E_WARNING, "Failed to open stream from socketpair");
-        RETURN_FALSE;        
+        RETURN_FALSE;
     }
 
     array_init(return_value);
@@ -1645,10 +1645,14 @@ PHP_FUNCTION(stream_isatty)
 
 	php_stream_from_zval(stream, zsrc);
 
-	if (php_stream_can_cast(stream, PHP_STREAM_AS_FD_FOR_SELECT) == SUCCESS) {
-		php_stream_cast(stream, PHP_STREAM_AS_FD_FOR_SELECT, (void*)&fileno, 0);
-	} else if (php_stream_can_cast(stream, PHP_STREAM_AS_FD) == SUCCESS) {
-		php_stream_cast(stream, PHP_STREAM_AS_FD, (void*)&fileno, 0);
+	/* get the fd.
+	 * NB: Most other code will NOT use the PHP_STREAM_CAST_INTERNAL flag when casting.
+	 * It is only used here so that the buffered data warning is not displayed.
+	 */
+	if (php_stream_can_cast(stream, PHP_STREAM_AS_FD_FOR_SELECT | PHP_STREAM_CAST_INTERNAL) == SUCCESS) {
+		php_stream_cast(stream, PHP_STREAM_AS_FD_FOR_SELECT | PHP_STREAM_CAST_INTERNAL, (void*)&fileno, 0);
+	} else if (php_stream_can_cast(stream, PHP_STREAM_AS_FD | PHP_STREAM_CAST_INTERNAL) == SUCCESS) {
+		php_stream_cast(stream, PHP_STREAM_AS_FD | PHP_STREAM_CAST_INTERNAL, (void*)&fileno, 0);
 	} else {
 		RETURN_FALSE;
 	}
@@ -1686,13 +1690,15 @@ PHP_FUNCTION(sapi_windows_vt100_support)
 
 	php_stream_from_zval(stream, zsrc);
 
-	if (php_stream_can_cast(stream, PHP_STREAM_AS_FD_FOR_SELECT) == SUCCESS) {
-		php_stream_cast(stream, PHP_STREAM_AS_FD_FOR_SELECT, (void*)&fileno, 0);
-	}
-	else if (php_stream_can_cast(stream, PHP_STREAM_AS_FD) == SUCCESS) {
-		php_stream_cast(stream, PHP_STREAM_AS_FD, (void*)&fileno, 0);
-	}
-	else {
+	/* get the fd.
+	 * NB: Most other code will NOT use the PHP_STREAM_CAST_INTERNAL flag when casting.
+	 * It is only used here so that the buffered data warning is not displayed.
+	 */
+	if (php_stream_can_cast(stream, PHP_STREAM_AS_FD_FOR_SELECT | PHP_STREAM_CAST_INTERNAL) == SUCCESS) {
+		php_stream_cast(stream, PHP_STREAM_AS_FD_FOR_SELECT | PHP_STREAM_CAST_INTERNAL, (void*)&fileno, 0);
+	} else if (php_stream_can_cast(stream, PHP_STREAM_AS_FD | PHP_STREAM_CAST_INTERNAL) == SUCCESS) {
+		php_stream_cast(stream, PHP_STREAM_AS_FD | PHP_STREAM_CAST_INTERNAL, (void*)&fileno, 0);
+	} else {
 		if (!enable_is_null) {
 			php_error_docref(
 				NULL,
diff --git a/ext/standard/tests/streams/stream_cast_loses_data.phpt b/ext/standard/tests/streams/stream_cast_loses_data.phpt
new file mode 100644
index 0000000000000..c2bcf9fd5914f
--- /dev/null
+++ b/ext/standard/tests/streams/stream_cast_loses_data.phpt
@@ -0,0 +1,37 @@
+--TEST--
+Casting a stream can lose data and needs to emit a warning
+--SKIPIF--
+<?php
+if (PHP_OS_FAMILY === "Windows") die("skip non-Windows tests (popen cannot delete file as open in cmd.exe)");
+?>
+--FILE--
+<?php
+
+$tempnam = tempnam(sys_get_temp_dir(), 'test');
+
+$stream = popen('echo 1; echo 2; rm ' . escapeshellarg($tempnam), 'r');
+
+do {
+    usleep(10);
+    clearstatcache();
+} while (file_exists($tempnam));
+
+// fills the read buffer with up to 8192 bytes
+fgets($stream);
+
+// cast $stream and read fd until eof. Print each line that was read, prefixed with "proc open stdin:"
+$process = proc_open(
+    'sed "s/^/proc open stdin:/"',
+    [
+        0 => $stream,
+        1 => ['pipe', 'w'],
+    ],
+    $pipes,
+);
+
+var_dump(stream_get_contents($pipes[1]));
+
+?>
+--EXPECTF--
+Warning: proc_open(): 2 bytes of buffered data lost during stream conversion! in %s on line %d
+string(0) ""
diff --git a/tests/output/DummyStreamWrapper.inc b/tests/output/DummyStreamWrapper.inc
new file mode 100644
index 0000000000000..664e07a884b2b
--- /dev/null
+++ b/tests/output/DummyStreamWrapper.inc
@@ -0,0 +1,61 @@
+<?php
+
+class DummyStreamWrapper
+{
+    /** @var resource|null */
+    public $context;
+
+    /** @var resource|null */
+    public $handle;
+
+    public function stream_cast(int $castAs)
+    {
+        return false;
+    }
+
+    public function stream_close(): void { }
+
+    public function stream_open(string $path, string $mode, int $options = 0, ?string &$openedPath = null): bool
+    {
+        return true;
+    }
+
+    public function stream_read(int $count)
+    {
+        return false;
+    }
+
+    public function stream_seek(int $offset, int $whence = SEEK_SET): bool
+    {
+        var_dump('stream_seek!');
+        return true;
+    }
+
+    public function stream_set_option(int $option, int $arg1, ?int $arg2): bool
+    {
+        return false;
+    }
+
+    public function stream_stat()
+    {
+        return false;
+    }
+
+    public function stream_tell()
+    {
+        return 0;
+    }
+
+    public function stream_truncate(int $newSize): bool
+    {
+        return true;
+    }
+
+    public function stream_write(string $data) { }
+
+
+    public function unlink(string $path): bool
+    {
+        return false;
+    }
+}
diff --git a/tests/output/sapi_windows_vt100_support_no_warning_on_cast.phpt b/tests/output/sapi_windows_vt100_support_no_warning_on_cast.phpt
new file mode 100644
index 0000000000000..1d303d8a9a73b
--- /dev/null
+++ b/tests/output/sapi_windows_vt100_support_no_warning_on_cast.phpt
@@ -0,0 +1,34 @@
+--TEST--
+sapi_windows_vt100_support(): casting stream does not emit data loss and should not emit warnings
+--SKIPIF--
+<?php
+if (PHP_OS_FAMILY !== "Windows") {
+    die("skip Only for Windows systems");
+}
+require __DIR__ . '/../../ext/standard/tests/http/server.inc'; http_server_skipif();
+?>
+--INI--
+allow_url_fopen=1
+--FILE--
+<?php
+
+require __DIR__ . '/../../ext/standard/tests/http/server.inc';
+
+$responses = array(
+    "data://text/plain,HTTP/1.0 200 Ok\r\nSome: Header\r\nSome: Header\r\n\r\nBody",
+);
+
+['pid' => $pid, 'uri' => $uri] = http_server($responses, $output);
+
+/* Note: the warning is bogus in this case as no data actually gets lost,
+ * but this checks that stream casting works */
+$handle = fopen($uri, 'r');
+var_dump(sapi_windows_vt100_support($handle));
+var_dump(fread($handle, 20));
+fclose($handle);
+
+http_server_kill($pid);
+?>
+--EXPECT--
+bool(false)
+string(4) "Body"
diff --git a/tests/output/sapi_windows_vt100_support_non_castable_user_stream.phpt b/tests/output/sapi_windows_vt100_support_non_castable_user_stream.phpt
new file mode 100644
index 0000000000000..b47a5fd51b6e5
--- /dev/null
+++ b/tests/output/sapi_windows_vt100_support_non_castable_user_stream.phpt
@@ -0,0 +1,27 @@
+--TEST--
+sapi_windows_vt100_support(): uncastable user stream
+--SKIPIF--
+<?php
+if (PHP_OS_FAMILY !== "Windows") {
+    die("skip Only for Windows systems");
+}
+?>
+--FILE--
+<?php
+
+require __DIR__ . '/DummyStreamWrapper.inc';
+stream_wrapper_register('custom', DummyStreamWrapper::class);
+
+$fp = fopen("custom://myvar", "r+");
+try {
+    var_dump(sapi_windows_vt100_support($fp));
+} catch (\TypeError $e) {
+    echo $e->getMessage(), PHP_EOL;
+}
+fclose($fp);
+
+echo "Done";
+?>
+--EXPECT--
+bool(false)
+Done
diff --git a/tests/output/stream_isatty_no_warning_on_cast.phpt b/tests/output/stream_isatty_no_warning_on_cast.phpt
new file mode 100644
index 0000000000000..3f0e184134fa8
--- /dev/null
+++ b/tests/output/stream_isatty_no_warning_on_cast.phpt
@@ -0,0 +1,32 @@
+--TEST--
+stream_isatty(): casting stream does not emit data loss and should not emit warnings
+Bug GH-10092 (Internal stream casting should not emit lost bytes warning twice)
+--SKIPIF--
+<?php
+require __DIR__ . '/../../ext/standard/tests/http/server.inc'; http_server_skipif();
+?>
+--INI--
+allow_url_fopen=1
+--FILE--
+<?php
+
+require __DIR__ . '/../../ext/standard/tests/http/server.inc';
+
+$responses = array(
+    "data://text/plain,HTTP/1.0 200 Ok\r\nSome: Header\r\nSome: Header\r\n\r\nBody",
+);
+
+['pid' => $pid, 'uri' => $uri] = http_server($responses, $output);
+
+/* Note: the warning is bogus in this case as no data actually gets lost,
+ * but this checks that stream casting works */
+$handle = fopen($uri, 'r');
+var_dump(stream_isatty($handle));
+var_dump(fread($handle, 20));
+fclose($handle);
+
+http_server_kill($pid);
+?>
+--EXPECT--
+bool(false)
+string(4) "Body"
diff --git a/tests/output/stream_isatty_non_castable_user_stream.phpt b/tests/output/stream_isatty_non_castable_user_stream.phpt
new file mode 100644
index 0000000000000..4c6c5b6503075
--- /dev/null
+++ b/tests/output/stream_isatty_non_castable_user_stream.phpt
@@ -0,0 +1,17 @@
+--TEST--
+stream_isatty(): uncastable user stream
+--FILE--
+<?php
+
+require __DIR__ . '/DummyStreamWrapper.inc';
+stream_wrapper_register('custom', DummyStreamWrapper::class);
+
+$fp = fopen("custom://myvar", "r+");
+var_dump(stream_isatty($fp));
+fclose($fp);
+
+echo "Done";
+?>
+--EXPECT--
+bool(false)
+Done