--- a/devtools/shared/protocol.js
+++ b/devtools/shared/protocol.js
@@ -113,26 +113,33 @@ types.getType = function(type) {
   if (pieces.length > 1) {
     return types.addActorDetail(type, pieces[0], pieces[1]);
   }
 
   throw Error("Unknown type: " + type);
 };
 
 /**
+ * Helper function to identify iterators. This will return false for Arrays.
+ */
+function isIterator(v) {
+  return v && typeof v === "object" && Symbol.iterator in v && !Array.isArray(v);
+}
+
+/**
  * Don't allow undefined when writing primitive types to packets.  If
  * you want to allow undefined, use a nullable type.
  */
 function identityWrite(v) {
   if (v === undefined) {
     throw Error("undefined passed where a value is required");
   }
   // This has to handle iterator->array conversion because arrays of
   // primitive types pass through here.
-  if (v && typeof (v) === "object" && Symbol.iterator in v) {
+  if (isIterator(v)) {
     return [...v];
   }
   return v;
 }
 
 /**
  * Add a type to the type system.
  *