diff --git a/ext/bg/js/backend.js b/ext/bg/js/backend.js
index 7d68ed84..01340419 100644
--- a/ext/bg/js/backend.js
+++ b/ext/bg/js/backend.js
@@ -71,7 +71,7 @@ class Backend {
             return promise.then(result => {
                 callback({result});
             }).catch(error => {
-                callback({error});
+                callback({error: error.toString ? error.toString() : error});
             });
         };
 
diff --git a/ext/bg/js/search.js b/ext/bg/js/search.js
index 54cda8ec..40bf2019 100644
--- a/ext/bg/js/search.js
+++ b/ext/bg/js/search.js
@@ -29,7 +29,7 @@ class DisplaySearch extends Display {
     }
 
     onError(error) {
-        window.alert(`Error: ${error}`);
+        window.alert(`Error: ${error.toString ? error.toString() : error}`);
     }
 
     onSearchClear() {
diff --git a/ext/fg/js/float.js b/ext/fg/js/float.js
index 22374f8b..ff50483d 100644
--- a/ext/fg/js/float.js
+++ b/ext/fg/js/float.js
@@ -27,7 +27,7 @@ class DisplayFloat extends Display {
         if (window.yomichan_orphaned) {
             this.onOrphaned();
         } else {
-            window.alert(`Error: ${error}`);
+            window.alert(`Error: ${error.toString ? error.toString() : error}`);
         }
     }
 
diff --git a/ext/fg/js/frontend.js b/ext/fg/js/frontend.js
index 63cdc25e..3a90b3ad 100644
--- a/ext/fg/js/frontend.js
+++ b/ext/fg/js/frontend.js
@@ -152,7 +152,7 @@ class Frontend {
     }
 
     onError(error) {
-        window.alert(`Error: ${error}`);
+        window.alert(`Error: ${error.toString ? error.toString() : error}`);
     }
 
     popupTimerSet(callback) {