--- a/gfx/thebes/gfxASurface.cpp
+++ b/gfx/thebes/gfxASurface.cpp
@@ -467,17 +467,17 @@ public:
     static void AdjustUsedMemory(gfxSurfaceType aType, int32_t aBytes)
     {
         // A read-modify-write operation like += would require a memory barrier
         // here, which would defeat the purpose of using relaxed memory
         // ordering.  So separate out the read and write operations.
         sSurfaceMemoryUsed[size_t(aType)] = sSurfaceMemoryUsed[size_t(aType)] + aBytes;
     };
 
-    NS_DECL_ISUPPORTS
+    NS_DECL_THREADSAFE_ISUPPORTS
 
     NS_IMETHOD CollectReports(nsIHandleReportCallback *aHandleReport,
                               nsISupports *aData, bool aAnonymize) override
     {
         const size_t len = ArrayLength(sSurfaceMemoryReporterAttrs);
         for (size_t i = 0; i < len; i++) {
             int64_t amount = sSurfaceMemoryUsed[i];