diff --git a/src/audio/SDL_audiocvt.c b/src/audio/SDL_audiocvt.c
index 831b36e8c5..644df39d5d 100644
--- a/src/audio/SDL_audiocvt.c
+++ b/src/audio/SDL_audiocvt.c
@@ -442,9 +442,11 @@ SDL_PropertiesID SDL_GetAudioStreamProperties(SDL_AudioStream *stream)
         SDL_InvalidParamError("stream");
         return 0;
     }
+    SDL_LockMutex(stream->lock);
     if (stream->props == 0) {
         stream->props = SDL_CreateProperties();
     }
+    SDL_UnlockMutex(stream->lock);
     return stream->props;
 }