diff --git a/ext/gd/libgd/gdft.c b/ext/gd/libgd/gdft.c
index 86dd8c3c771..499de8637b2 100644
--- a/ext/gd/libgd/gdft.c
+++ b/ext/gd/libgd/gdft.c
@@ -721,6 +721,7 @@ void gdFontCacheShutdown()
 		gdMutexLock(gdFontCacheMutex);
 		gdCacheDelete(fontCache);
 		fontCache = NULL;
+		gdMutexUnlock(gdFontCacheMutex);
 		gdMutexShutdown(gdFontCacheMutex);
 		FT_Done_FreeType(library);
 	}