--- a/devtools/server/actors/script.js
+++ b/devtools/server/actors/script.js
@@ -2009,17 +2009,19 @@ const ThreadActor = ActorClass({
       // has not completed yet.
       //
       // The root of the problem is that unsafeSynchronize can cause debuggee
       // code to run. Unfortunately, fixing that is prohibitively difficult. The
       // best we can do at the moment is disable source maps for the browser
       // debugger, and carefully avoid the use of unsafeSynchronize in this
       // function when source maps are disabled.
       for (let actor of bpActors) {
-        actor.originalLocation.originalSourceActor._setBreakpoint(actor);
+        if (actor.isPending) {
+          actor.originalLocation.originalSourceActor._setBreakpoint(actor);
+        }
       }
     }
 
     this._debuggerSourcesSeen.add(aSource);
     return true;
   },