3 files changed, 11 insertions, 5 deletions
diff --git a/src/wasm/wasm-binary.cpp b/src/wasm/wasm-binary.cpp
index 920baf944..bc7ec8ac8 100644
--- a/src/wasm/wasm-binary.cpp
+++ b/src/wasm/wasm-binary.cpp
@@ -1544,9 +1544,9 @@ void WasmBinaryWriter::writeInlineBuffer(const char* data, size_t size) {
 
 void WasmBinaryWriter::writeType(Type type) {
   if (type.isRef()) {
-    // The only reference types allowed without GC are funcref and externref. We
-    // internally use more refined versions of those types, but we cannot emit
-    // those more refined types.
+    // The only reference types allowed without GC are funcref, externref, and
+    // exnref. We internally use more refined versions of those types, but we
+    // cannot emit those without GC.
     if (!wasm->features.hasGC()) {
       auto ht = type.getHeapType();
       if (ht.isMaybeShared(HeapType::string)) {
@@ -1555,6 +1555,8 @@ void WasmBinaryWriter::writeType(Type type) {
         // string, the stringref feature must be enabled.
         type = Type(HeapTypes::string.getBasic(ht.getShared()), Nullable);
       } else {
+        // Only the top type (func, extern, exn) is available, and only the
+        // nullable version.
         type = Type(type.getHeapType().getTop(), Nullable);
       }
     }
diff --git a/src/wasm/wasm-validator.cpp b/src/wasm/wasm-validator.cpp
index a86187fa7..0184e3284 100644
--- a/src/wasm/wasm-validator.cpp
+++ b/src/wasm/wasm-validator.cpp
@@ -2658,7 +2658,7 @@ void FunctionValidator::visitTryTable(TryTable* curr) {
                 "the number of catch tags and sent types do not match");
 
   const char* invalidSentTypeMsg = "invalid catch sent type information";
-  Type exnref = Type(HeapType::exn, Nullable);
+  Type exnref = Type(HeapType::exn, NonNullable);
   for (Index i = 0; i < curr->catchTags.size(); i++) {
     auto sentType = curr->sentTypes[i];
     size_t tagTypeSize;
diff --git a/src/wasm/wasm.cpp b/src/wasm/wasm.cpp
index 0245fc01e..4150af5b4 100644
--- a/src/wasm/wasm.cpp
+++ b/src/wasm/wasm.cpp
@@ -933,7 +933,11 @@ static void populateTryTableSentTypes(TryTable* curr, Module* wasm) {
     return;
   }
   curr->sentTypes.clear();
-  Type exnref = Type(HeapType::exn, Nullable);
+  // We always use the refined non-nullable type in our IR, which is what the
+  // wasm spec defines when GC is enabled (=== non-nullable types are allowed).
+  // If GC is not enabled then we emit a nullable type in the binary format in
+  // WasmBinaryWriter::writeType.
+  Type exnref = Type(HeapType::exn, NonNullable);
   for (Index i = 0; i < curr->catchTags.size(); i++) {
     auto tagName = curr->catchTags[i];
     std::vector<Type> sentType;