--- a/mfbt/Vector.h
+++ b/mfbt/Vector.h
@@ -719,18 +719,16 @@ VectorBase<T, N, AP, TV>::convertToHeapS
   return true;
 }
 
 template<typename T, size_t N, class AP, class TV>
 MOZ_NEVER_INLINE bool
 VectorBase<T, N, AP, TV>::growStorageBy(size_t aIncr)
 {
   MOZ_ASSERT(mLength + aIncr > mCapacity);
-  MOZ_ASSERT_IF(!usingInlineStorage(),
-                !detail::CapacityHasExcessSpace<T>(mCapacity));
 
   /*
    * When choosing a new capacity, its size should is as close to 2**N bytes
    * as possible.  2**N-sized requests are best because they are unlikely to
    * be rounded up by the allocator.  Asking for a 2**N number of elements
    * isn't as good, because if sizeof(T) is not a power-of-two that would
    * result in a non-2**N request size.
    */