diff --git a/backend/api-renamed/gist.js b/backend/api-renamed/gist.js
index 19a6c1b8..be343d28 100644
--- a/backend/api-renamed/gist.js
+++ b/backend/api-renamed/gist.js
@@ -12,7 +12,9 @@ import {
   setErrorCacheHeaders,
 } from "../src/common/cache.js";
 import { guardAccess } from "../src/common/access.js";
+import { retrieveSecondaryMessage } from "../src/common/error.js";
 
+// @ts-ignore
 export default async (req, res) => {
   const {
     id,
@@ -91,10 +93,24 @@ export default async (req, res) => {
     );
   } catch (err) {
     setErrorCacheHeaders(res);
+    if (err instanceof Error) {
+      return res.send(
+        renderError({
+          message: err.message,
+          secondaryMessage: retrieveSecondaryMessage(err),
+          renderOptions: {
+            title_color,
+            text_color,
+            bg_color,
+            border_color,
+            theme,
+          },
+        }),
+      );
+    }
     return res.send(
       renderError({
-        message: err.message,
-        secondaryMessage: err.secondaryMessage,
+        message: "An unknown error occurred",
         renderOptions: {
           title_color,
           text_color,
diff --git a/backend/api-renamed/pin.js b/backend/api-renamed/pin.js
index a71fe43f..86e53201 100644
--- a/backend/api-renamed/pin.js
+++ b/backend/api-renamed/pin.js
@@ -8,11 +8,13 @@ import {
   setCacheHeaders,
   setErrorCacheHeaders,
 } from "../src/common/cache.js";
+import { retrieveSecondaryMessage } from "../src/common/error.js";
 import { parseArray, parseBoolean, renderError } from "../src/common/utils.js";
 import { fetchRepo } from "../src/fetchers/repo.js";
 import { isLocaleAvailable } from "../src/translations.js";
 import { storeRequest } from "../src/common/database.js";
 
+// @ts-ignore
 export default async (req, res) => {
   const {
     username,
@@ -138,10 +140,24 @@ export default async (req, res) => {
     );
   } catch (err) {
     setErrorCacheHeaders(res);
+    if (err instanceof Error) {
+      return res.send(
+        renderError({
+          message: err.message,
+          secondaryMessage: retrieveSecondaryMessage(err),
+          renderOptions: {
+            title_color,
+            text_color,
+            bg_color,
+            border_color,
+            theme,
+          },
+        }),
+      );
+    }
     return res.send(
       renderError({
-        message: err.message,
-        secondaryMessage: err.secondaryMessage,
+        message: "An unknown error occurred",
         renderOptions: {
           title_color,
           text_color,
diff --git a/backend/api-renamed/top-langs.js b/backend/api-renamed/top-langs.js
index 77158435..1ca52d21 100644
--- a/backend/api-renamed/top-langs.js
+++ b/backend/api-renamed/top-langs.js
@@ -8,11 +8,13 @@ import {
   setCacheHeaders,
   setErrorCacheHeaders,
 } from "../src/common/cache.js";
+import { retrieveSecondaryMessage } from "../src/common/error.js";
 import { parseArray, parseBoolean, renderError } from "../src/common/utils.js";
 import { fetchTopLanguages } from "../src/fetchers/top-languages.js";
 import { isLocaleAvailable } from "../src/translations.js";
 import { storeRequest } from "../src/common/database.js";
 
+// @ts-ignore
 export default async (req, res) => {
   const {
     username,
@@ -154,10 +156,24 @@ export default async (req, res) => {
     );
   } catch (err) {
     setErrorCacheHeaders(res);
+    if (err instanceof Error) {
+      return res.send(
+        renderError({
+          message: err.message,
+          secondaryMessage: retrieveSecondaryMessage(err),
+          renderOptions: {
+            title_color,
+            text_color,
+            bg_color,
+            border_color,
+            theme,
+          },
+        }),
+      );
+    }
     return res.send(
       renderError({
-        message: err.message,
-        secondaryMessage: err.secondaryMessage,
+        message: "An unknown error occurred",
         renderOptions: {
           title_color,
           text_color,
diff --git a/backend/api-renamed/wakatime.js b/backend/api-renamed/wakatime.js
index 28bbab6b..1dfd5ebe 100644
--- a/backend/api-renamed/wakatime.js
+++ b/backend/api-renamed/wakatime.js
@@ -12,7 +12,9 @@ import {
   setErrorCacheHeaders,
 } from "../src/common/cache.js";
 import { guardAccess } from "../src/common/access.js";
+import { retrieveSecondaryMessage } from "../src/common/error.js";
 
+// @ts-ignore
 export default async (req, res) => {
   const {
     username,
@@ -110,10 +112,24 @@ export default async (req, res) => {
     );
   } catch (err) {
     setErrorCacheHeaders(res);
+    if (err instanceof Error) {
+      return res.send(
+        renderError({
+          message: err.message,
+          secondaryMessage: retrieveSecondaryMessage(err),
+          renderOptions: {
+            title_color,
+            text_color,
+            bg_color,
+            border_color,
+            theme,
+          },
+        }),
+      );
+    }
     return res.send(
       renderError({
-        message: err.message,
-        secondaryMessage: err.secondaryMessage,
+        message: "An unknown error occurred",
         renderOptions: {
           title_color,
           text_color,
diff --git a/backend/src/common/error.js b/backend/src/common/error.js
index 2035fb20..3f8a1104 100644
--- a/backend/src/common/error.js
+++ b/backend/src/common/error.js
@@ -1,3 +1,5 @@
+// @ts-check
+
 import { OWNER_AFFILIATIONS } from "./utils.js";
 
 /**
@@ -67,9 +69,22 @@ class MissingParamError extends Error {
   }
 }
 
+/**
+ * Retrieve secondary message from an error object.
+ *
+ * @param {Error} err The error object.
+ * @returns {string|undefined} The secondary message if available, otherwise undefined.
+ */
+const retrieveSecondaryMessage = (err) => {
+  return "secondaryMessage" in err && typeof err.secondaryMessage === "string"
+    ? err.secondaryMessage
+    : undefined;
+};
+
 export {
   CustomError,
   MissingParamError,
   SECONDARY_ERROR_MESSAGES,
   TRY_AGAIN_LATER,
+  retrieveSecondaryMessage,
 };