new file mode 100644
--- /dev/null
+++ b/js/src/jit-test/tests/debug/bug1331064.js
@@ -0,0 +1,22 @@
+// |jit-test| test-also-wasm-baseline; exitstatus: 3
+
+load(libdir + "asserts.js");
+
+if (!wasmIsSupported())
+     quit(3);
+
+var g = newGlobal();
+g.parent = this;
+g.eval("new Debugger(parent).onExceptionUnwind = function () {  some_error; };");
+
+var module = new WebAssembly.Module(wasmTextToBinary(`
+(module
+    (import $imp "a" "b" (result i32))
+    (func $call (result i32) (call 0))
+    (export "call" $call)
+)`));
+
+var instance = new WebAssembly.Instance(module, { a: { b: () => {
+  some_other_error;
+}}});
+instance.exports.call();

--- a/js/src/wasm/WasmTypes.cpp
+++ b/js/src/wasm/WasmTypes.cpp
@@ -146,22 +146,26 @@ WasmHandleThrow()
     JSContext* cx = activation->cx();
 
     for (FrameIterator iter(activation, FrameIterator::Unwind::True); !iter.done(); ++iter) {
         if (!iter.debugEnabled())
             continue;
 
         DebugFrame* frame = iter.debugFrame();
 
-        JSTrapStatus status = Debugger::onExceptionUnwind(cx, frame);
-        if (status == JSTRAP_RETURN) {
-            // Unexpected trap return -- raising error since throw recovery
-            // is not yet implemented in the wasm baseline.
-            // TODO properly handle JSTRAP_RETURN and resume wasm execution.
-            JS_ReportErrorASCII(cx, "Unexpected resumption value from onExceptionUnwind");
+        // Assume JSTRAP_ERROR status if no exception is pending --
+        // no onExceptionUnwind handlers must be fired.
+        if (cx->isExceptionPending()) {
+            JSTrapStatus status = Debugger::onExceptionUnwind(cx, frame);
+            if (status == JSTRAP_RETURN) {
+                // Unexpected trap return -- raising error since throw recovery
+                // is not yet implemented in the wasm baseline.
+                // TODO properly handle JSTRAP_RETURN and resume wasm execution.
+                JS_ReportErrorASCII(cx, "Unexpected resumption value from onExceptionUnwind");
+            }
         }
 
         bool ok = Debugger::onLeaveFrame(cx, frame, nullptr, false);
         if (ok) {
             // Unexpected success from the handler onLeaveFrame -- raising error
             // since throw recovery is not yet implemented in the wasm baseline.
             // TODO properly handle success and resume wasm execution.
             JS_ReportErrorASCII(cx, "Unexpected success from onLeaveFrame");