diff --git a/js/xpconnect/src/XPCWrappedJSClass.cpp b/js/xpconnect/src/XPCWrappedJSClass.cpp
index 594b186d529c..d469d4c48ac7 100644
--- a/js/xpconnect/src/XPCWrappedJSClass.cpp
+++ b/js/xpconnect/src/XPCWrappedJSClass.cpp
@@ -586,6 +586,29 @@ nsXPCWrappedJSClass::DelegatedQueryInterface(nsXPCWrappedJS* self,
         return NS_OK;
     }
 
+    // If we're asked to QI to nsISimpleEnumerator and the wrapped object does not have a
+    // QueryInterface method, assume it is a JS iterator, and wrap it into an equivalent
+    // nsISimpleEnumerator.
+    if (aIID.Equals(NS_GET_IID(nsISimpleEnumerator))) {
+        bool found;
+        XPCJSContext* xpccx = ccx.GetContext();
+        if (JS_HasPropertyById(aes.cx(), obj,
+                               xpccx->GetStringID(xpccx->IDX_QUERY_INTERFACE),
+                               &found) && !found) {
+            nsresult rv;
+            nsCOMPtr<nsIJSEnumerator> jsEnum;
+            if (!XPCConvert::JSObject2NativeInterface(aes.cx(),
+                                                      getter_AddRefs(jsEnum), obj,
+                                                      &NS_GET_IID(nsIJSEnumerator),
+                                                      nullptr, &rv)) {
+                return rv;
+            }
+            nsCOMPtr<nsISimpleEnumerator> res = new XPCWrappedJSIterator(jsEnum);
+            res.forget(aInstancePtr);
+            return NS_OK;
+        }
+    }
+
     // Checks for any existing wrapper explicitly constructed for this iid.
     // This includes the current 'self' wrapper. This also deals with the
     // nsISupports case (for which it returns mRoot).
@@ -611,29 +634,6 @@ nsXPCWrappedJSClass::DelegatedQueryInterface(nsXPCWrappedJS* self,
         return rv;
     }
 
-    // If we're asked to QI to nsISimpleEnumerator and the wrapped object does not have a
-    // QueryInterface method, assume it is a JS iterator, and wrap it into an equivalent
-    // nsISimpleEnumerator.
-    if (aIID.Equals(NS_GET_IID(nsISimpleEnumerator))) {
-        bool found;
-        XPCJSContext* xpccx = ccx.GetContext();
-        if (JS_HasPropertyById(aes.cx(), obj,
-                               xpccx->GetStringID(xpccx->IDX_QUERY_INTERFACE),
-                               &found) && !found) {
-            nsresult rv;
-            nsCOMPtr<nsIJSEnumerator> jsEnum;
-            if (!XPCConvert::JSObject2NativeInterface(aes.cx(),
-                                                      getter_AddRefs(jsEnum), obj,
-                                                      &NS_GET_IID(nsIJSEnumerator),
-                                                      nullptr, &rv)) {
-                return rv;
-            }
-            nsCOMPtr<nsISimpleEnumerator> res = new XPCWrappedJSIterator(jsEnum);
-            res.forget(aInstancePtr);
-            return NS_OK;
-        }
-    }
-
     // else we do the more expensive stuff...
 
     // check if the JSObject claims to implement this interface
diff --git a/js/xpconnect/tests/unit/test_wrapped_js_enumerator.js b/js/xpconnect/tests/unit/test_wrapped_js_enumerator.js
index 55adfffdf1fb..643acf504545 100644
--- a/js/xpconnect/tests/unit/test_wrapped_js_enumerator.js
+++ b/js/xpconnect/tests/unit/test_wrapped_js_enumerator.js
@@ -9,12 +9,24 @@ const Variant = Components.Constructor("@mozilla.org/variant;1",
 const SupportsInterfacePointer = Components.Constructor(
   "@mozilla.org/supports-interface-pointer;1", "nsISupportsInterfacePointer");
 
-function wrapEnumerator(iter) {
+function wrapEnumerator1(iter) {
   var ip = SupportsInterfacePointer();
   ip.data = iter;
   return ip.data.QueryInterface(Ci.nsISimpleEnumerator);
 }
 
+function wrapEnumerator2(iter) {
+  var ip = SupportsInterfacePointer();
+  ip.data = {
+    QueryInterface: ChromeUtils.generateQI([Ci.nsIFilePicker]),
+    get files() {
+      return iter;
+    },
+  };
+  return ip.data.QueryInterface(Ci.nsIFilePicker).files;
+}
+
+
 function enumToArray(iter) {
   let result = [];
   while (iter.hasMoreElements()) {
@@ -26,32 +38,34 @@ function enumToArray(iter) {
 add_task(async function test_wrapped_js_enumerator() {
   let array = [1, 2, 3, 4];
 
-  // Test a plain JS iterator. This should automatically be wrapped into
-  // an equivalent nsISimpleEnumerator.
-  {
-    let iter = wrapEnumerator(array.values());
-    let result = enumToArray(iter);
+  for (let wrapEnumerator of [wrapEnumerator1, wrapEnumerator2]) {
+    // Test a plain JS iterator. This should automatically be wrapped into
+    // an equivalent nsISimpleEnumerator.
+    {
+      let iter = wrapEnumerator(array.values());
+      let result = enumToArray(iter);
 
-    deepEqual(result, array, "Got correct result");
-  }
+      deepEqual(result, array, "Got correct result");
+    }
 
-  // Test an object with a QueryInterface method, which implements
-  // nsISimpleEnumerator. This should be wrapped and used directly.
-  {
-    let obj = {
-      QueryInterface: ChromeUtils.generateQI(["nsISimpleEnumerator"]),
-      _idx: 0,
-      hasMoreElements() {
-        return this._idx < array.length;
-      },
-      getNext() {
-        return Variant(array[this._idx++]);
-      },
-    };
+    // Test an object with a QueryInterface method, which implements
+    // nsISimpleEnumerator. This should be wrapped and used directly.
+    {
+      let obj = {
+        QueryInterface: ChromeUtils.generateQI(["nsISimpleEnumerator"]),
+        _idx: 0,
+        hasMoreElements() {
+          return this._idx < array.length;
+        },
+        getNext() {
+          return Variant(array[this._idx++]);
+        },
+      };
 
-    let iter = wrapEnumerator(obj);
-    let result = enumToArray(iter);
+      let iter = wrapEnumerator(obj);
+      let result = enumToArray(iter);
 
-    deepEqual(result, array, "Got correct result");
+      deepEqual(result, array, "Got correct result");
+    }
   }
 });