diff --git a/src/heap/cppgc-js/cpp-heap.cc b/src/heap/cppgc-js/cpp-heap.cc
index ec5aa5382e..c0c18e5b34 100644
--- a/src/heap/cppgc-js/cpp-heap.cc
+++ b/src/heap/cppgc-js/cpp-heap.cc
@@ -75,7 +75,9 @@ class V8ToCppGCReferencesVisitor final
 
     const internal::JSObject js_object =
         *reinterpret_cast<const internal::JSObject* const&>(value);
-    if (!js_object.ptr() || !js_object.MayHaveEmbedderFields()) return;
+    if (!js_object.ptr() || js_object.IsSmi() ||
+        !js_object.MayHaveEmbedderFields())
+      return;
 
     internal::LocalEmbedderHeapTracer::WrapperInfo info;
     if (!internal::LocalEmbedderHeapTracer::ExtractWrappableInfo(