1 files changed, 8 insertions, 2 deletions
diff --git a/src/wasm/wasm-stack.cpp b/src/wasm/wasm-stack.cpp
index c4b9598c7..db40a5980 100644
--- a/src/wasm/wasm-stack.cpp
+++ b/src/wasm/wasm-stack.cpp
@@ -2033,10 +2033,16 @@ void BinaryInstWriter::visitRefCast(RefCast* curr) {
   o << int8_t(BinaryConsts::GCPrefix);
   if (curr->safety == RefCast::Unsafe) {
     o << U32LEB(BinaryConsts::RefCastNop);
+    parent.writeIndexedHeapType(curr->intendedType);
   } else {
-    o << U32LEB(BinaryConsts::RefCastNull);
+    // Emulate legacy polymorphic behavior for now.
+    if (curr->ref->type.isNullable()) {
+      o << U32LEB(BinaryConsts::RefCastNull);
+    } else {
+      o << U32LEB(BinaryConsts::RefCast);
+    }
+    parent.writeHeapType(curr->intendedType);
   }
-  parent.writeHeapType(curr->intendedType);
 }
 
 void BinaryInstWriter::visitBrOn(BrOn* curr) {