diff --git a/browser/devtools/inspector/inspector-panel.js b/browser/devtools/inspector/inspector-panel.js
index e55ed90095db..7416acd2caff 100644
--- a/browser/devtools/inspector/inspector-panel.js
+++ b/browser/devtools/inspector/inspector-panel.js
@@ -515,7 +515,11 @@ InspectorPanel.prototype = {
     if (this.walker) {
       this.walker.off("new-root", this.onNewRoot);
       this._destroyPromise = this.walker.release()
-        .then(() => this._inspector.destroy())
+        .then(() => this._inspector.destroy(),
+              (e) => {
+                console.error("Walker.release() failed: " + e);
+                return this._inspector.destroy();
+              })
         .then(() => {
           this._inspector = null;
         }, console.error);
diff --git a/toolkit/devtools/server/protocol.js b/toolkit/devtools/server/protocol.js
index 4bfe63ba2240..9632e75ec846 100644
--- a/toolkit/devtools/server/protocol.js
+++ b/toolkit/devtools/server/protocol.js
@@ -1058,7 +1058,7 @@ let Front = Class({
 
     // Remaining packets must be responses.
     if (this._requests.length === 0) {
-      let msg = "Unexpected packet from " + this.actorID + ", " + packet.type;
+      let msg = "Unexpected packet " + this.actorID + ", " + JSON.stringify(packet);
       let err = Error(msg);
       console.error(err);
       throw err;