diff --git a/NEWS b/NEWS
index 999d1f6fc5ae..3cc806719d59 100644
--- a/NEWS
+++ b/NEWS
@@ -18,6 +18,10 @@ PHP                                                                        NEWS
   . Fixed chown() and lchown() failing to resolve user names in ZTS builds
     when getpwnam_r() needs a larger buffer. (Ilia Alshanetsky)
 
+- Streams:
+  . Fixed bug GH-24173 (Sockets from synchronous stream_socket_client() are
+    left in non-blocking mode on Windows). (vibbow)
+
 22 Oct 2026, PHP 8.4.27
 
 - BCMath:
diff --git a/ext/standard/tests/streams/gh24173.phpt b/ext/standard/tests/streams/gh24173.phpt
new file mode 100644
index 000000000000..feaf5ce46260
--- /dev/null
+++ b/ext/standard/tests/streams/gh24173.phpt
@@ -0,0 +1,25 @@
+--TEST--
+GH-24173 (Sockets from synchronous stream_socket_client() are left in non-blocking mode on Windows)
+--EXTENSIONS--
+sockets
+--SKIPIF--
+<?php
+if (PHP_OS_FAMILY !== 'Windows') die('skip Windows only');
+?>
+--FILE--
+<?php
+$srv = stream_socket_server('tcp://127.0.0.1:0', $errno, $errstr);
+$client = stream_socket_client('tcp://' . stream_socket_get_name($srv, false), $errno, $errstr, 5);
+$conn = stream_socket_accept($srv);
+
+$sock = socket_import_stream($client);
+socket_set_option($sock, SOL_SOCKET, SO_RCVTIMEO, ['sec' => 0, 'usec' => 100000]);
+
+// No data is sent: a blocking socket waits and times out, while a
+// non-blocking one fails at once with WSAEWOULDBLOCK.
+var_dump(@socket_read($sock, 10));
+var_dump(socket_last_error($sock) === SOCKET_ETIMEDOUT);
+?>
+--EXPECT--
+bool(false)
+bool(true)
diff --git a/ext/standard/tests/streams/gh24173_write_timeout.phpt b/ext/standard/tests/streams/gh24173_write_timeout.phpt
new file mode 100644
index 000000000000..85babba8db2a
--- /dev/null
+++ b/ext/standard/tests/streams/gh24173_write_timeout.phpt
@@ -0,0 +1,31 @@
+--TEST--
+GH-24173 (Timed writes on socket streams must not block past the timeout)
+--SKIPIF--
+<?php
+if (PHP_OS_FAMILY !== 'Windows') die('skip Windows only');
+?>
+--FILE--
+<?php
+$srv = stream_socket_server('tcp://127.0.0.1:0', $errno, $errstr);
+$client = stream_socket_client('tcp://' . stream_socket_get_name($srv, false), $errno, $errstr, 5);
+$conn = stream_socket_accept($srv);
+
+// Neither side reads, so writes eventually fill the socket buffers. A write
+// that times out may still have written part of the chunk, so stop at the
+// first timeout rather than at the first zero-length write.
+$chunk = str_repeat('x', 1 << 20);
+foreach (['client' => $client, 'accepted' => $conn] as $name => $stream) {
+    stream_set_timeout($stream, 0, 200000);
+    for ($i = 0; $i < 256; $i++) {
+        @fwrite($stream, $chunk);
+        if (stream_get_meta_data($stream)['timed_out']) {
+            break;
+        }
+    }
+    echo $name, ': ';
+    var_dump(stream_get_meta_data($stream)['timed_out']);
+}
+?>
+--EXPECT--
+client: bool(true)
+accepted: bool(true)
diff --git a/main/network.c b/main/network.c
index 40a80a6f2abc..e6e4c96d5624 100644
--- a/main/network.c
+++ b/main/network.c
@@ -286,8 +286,10 @@ PHPAPI int php_network_getaddresses(const char *host, int socktype, struct socka
 typedef u_long php_non_blocking_flags_t;
 #  define SET_SOCKET_BLOCKING_MODE(sock, save) \
 	save = TRUE; ioctlsocket(sock, FIONBIO, &save)
+/* Winsock cannot query the current mode; callers pass freshly created
+ * (blocking) sockets, so restore to blocking. */
 #  define RESTORE_SOCKET_BLOCKING_MODE(sock, save) \
-	ioctlsocket(sock, FIONBIO, &save)
+	save = FALSE; ioctlsocket(sock, FIONBIO, &save)
 #else
 typedef int php_non_blocking_flags_t;
 #  define SET_SOCKET_BLOCKING_MODE(sock, save) \
diff --git a/main/streams/xp_socket.c b/main/streams/xp_socket.c
index 69eb078323be..aa5fd53ae7e9 100644
--- a/main/streams/xp_socket.c
+++ b/main/streams/xp_socket.c
@@ -69,6 +69,13 @@ static ssize_t php_sockop_write(php_stream *stream, const char *buf, size_t coun
 	else
 		ptimeout = &sock->timeout;
 
+#ifdef PHP_WIN32
+	/* There is no MSG_DONTWAIT on Windows, so switch to non-blocking mode for a
+	 * timed write; otherwise send() could block past the timeout. */
+	bool restore_blocking = sock->is_blocked && ptimeout
+		&& php_set_sock_blocking(sock->socket, 0) == SUCCESS;
+#endif
+
 retry:
 	didwrite = send(sock->socket, buf, XP_SOCK_BUF_SIZE(count), (sock->is_blocked && ptimeout) ? MSG_DONTWAIT : 0);
 
@@ -113,6 +120,12 @@ static ssize_t php_sockop_write(php_stream *stream, const char *buf, size_t coun
 		}
 	}
 
+#ifdef PHP_WIN32
+	if (restore_blocking) {
+		php_set_sock_blocking(sock->socket, 1);
+	}
+#endif
+
 	if (didwrite > 0) {
 		php_stream_notify_progress_increment(PHP_STREAM_CONTEXT(stream), didwrite, 0);
 	}