diff --git a/NEWS b/NEWS
index 6d317e7507f..a2c4da767ec 100644
--- a/NEWS
+++ b/NEWS
@@ -10,6 +10,10 @@ PHP                                                                        NEWS
 - Intl:
   . datefmt_parse/datefmt_localtime references type system fixes. (nielsdos)
 
+- Opcache:
+  . Fixed bug GH-18417 (Windows SHM reattachment fails when increasing
+    memory_consumption or jit_buffer_size). (nielsdos)
+
 - SPL:
   . Fixed bug GH-18421 (Integer overflow with large numbers in LimitIterator).
     (nielsdos)
diff --git a/ext/opcache/shared_alloc_win32.c b/ext/opcache/shared_alloc_win32.c
index 893fe98ec18..b24401e3d30 100644
--- a/ext/opcache/shared_alloc_win32.c
+++ b/ext/opcache/shared_alloc_win32.c
@@ -69,9 +69,9 @@ static void zend_win_error_message(int type, char *msg, int err)
 	php_win32_error_msg_free(buf);
 }
 
-static char *create_name_with_username(char *name)
+static char *create_name_with_username(const char *name, size_t unique_id)
 {
-	static char newname[MAXPATHLEN + 1 + 32 + 1 + 20 + 1 + 32 + 1];
+	static char newname[MAXPATHLEN + 1 + 32 + 1 + 20 + 1 + 32 + sizeof("ffffffffffffffff")-1 + 1];
 	char *p = newname;
 	p += strlcpy(newname, name, MAXPATHLEN + 1);
 	*(p++) = '@';
@@ -82,7 +82,11 @@ static char *create_name_with_username(char *name)
 	*(p++) = '@';
 	memcpy(p, zend_system_id, 32);
 	p += 32;
-	*(p++) = '\0';
+	if (unique_id) {
+		p += snprintf(p, sizeof("ffffffffffffffff"), "%zx", unique_id) + 1;
+	} else {
+		*(p++) = '\0';
+	}
 	ZEND_ASSERT(p - newname <= sizeof(newname));
 
 	return newname;
@@ -90,7 +94,7 @@ static char *create_name_with_username(char *name)
 
 void zend_shared_alloc_create_lock(void)
 {
-	memory_mutex = CreateMutex(NULL, FALSE, create_name_with_username(ACCEL_MUTEX_NAME));
+	memory_mutex = CreateMutex(NULL, FALSE, create_name_with_username(ACCEL_MUTEX_NAME, 0));
 	if (!memory_mutex) {
 		zend_accel_error(ACCEL_LOG_FATAL, "Cannot create mutex (error %u)", GetLastError());
 		return;
@@ -224,7 +228,7 @@ static int create_segments(size_t requested_size, zend_shared_segment ***shared_
 	   can be called before the child process is killed. In this case, the mapping will fail
 	   and we have to sleep some time (until the child releases the mapping object) and retry.*/
 	do {
-		memfile = OpenFileMapping(FILE_MAP_READ|FILE_MAP_WRITE|FILE_MAP_EXECUTE, 0, create_name_with_username(ACCEL_FILEMAP_NAME));
+		memfile = OpenFileMapping(FILE_MAP_READ|FILE_MAP_WRITE|FILE_MAP_EXECUTE, 0, create_name_with_username(ACCEL_FILEMAP_NAME, requested_size));
 		if (memfile == NULL) {
 			err = GetLastError();
 			break;
@@ -269,7 +273,7 @@ static int create_segments(size_t requested_size, zend_shared_segment ***shared_
 	(*shared_segments_p)[0] = shared_segment;
 
 	memfile	= CreateFileMapping(INVALID_HANDLE_VALUE, NULL, PAGE_EXECUTE_READWRITE | SEC_COMMIT, size_high, size_low,
-								create_name_with_username(ACCEL_FILEMAP_NAME));
+								create_name_with_username(ACCEL_FILEMAP_NAME, requested_size));
 	if (memfile == NULL) {
 		err = GetLastError();
 		zend_shared_alloc_unlock_win32();
diff --git a/ext/opcache/tests/gh18417.phpt b/ext/opcache/tests/gh18417.phpt
new file mode 100644
index 00000000000..e7b9790b9e6
--- /dev/null
+++ b/ext/opcache/tests/gh18417.phpt
@@ -0,0 +1,40 @@
+--TEST--
+GH-18417 (Windows SHM reattachment fails when increasing memory_consumption or jit_buffer_size)
+--SKIPIF--
+<?php
+$extDir = ini_get('extension_dir');
+if (!file_exists($extDir . '/php_opcache.dll')) {
+    die('skip Opcache DLL not found in extension_dir (Windows-only)');
+}
+?>
+--FILE--
+<?php
+$memory_consumption = (int) ini_get("opcache.memory_consumption");
+$new_memory_consumption = $memory_consumption * 2;
+$extension_dir = ini_get("extension_dir");
+
+$descriptorspec = [
+    0 => ["pipe", "r"],
+    1 => ["pipe", "w"],
+    2 => ["pipe", "w"],
+];
+
+$proc = proc_open([
+    PHP_BINARY,
+    "-n",
+    "-d", "extension_dir=$extension_dir",
+    "-d", "zend_extension=opcache",
+    "-d", "opcache.memory_consumption=$new_memory_consumption",
+    "-d", "opcache.enable=1",
+    "-d", "opcache.enable_cli=1",
+    "-r",
+    "echo 1;"
+], $descriptorspec, $pipes);
+
+echo stream_get_contents($pipes[1]);
+echo stream_get_contents($pipes[2]);
+
+proc_close($proc);
+?>
+--EXPECT--
+1