diff --git a/content/canvas/src/WebGLQuery.cpp b/content/canvas/src/WebGLQuery.cpp
index 8785d6899f18..0f187c029364 100644
--- a/content/canvas/src/WebGLQuery.cpp
+++ b/content/canvas/src/WebGLQuery.cpp
@@ -40,7 +40,7 @@ bool WebGLQuery::IsActive() const
 
     MOZ_ASSERT(targetSlot, "unknown query object's type");
 
-    return *targetSlot == this;
+    return targetSlot && *targetSlot == this;
 }