diff --git a/src/server.ts b/src/server.ts
index 7710088d..5a18d49d 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -43,6 +43,18 @@ export function getServer(
 
   // Express middleware
 
+  // Return 400 for URls containing non UTF-8 encoded chars 
+ app.use((req, res, next) => {
+  const pathOnly = req.url.split('?')[0].split('#')[0];
+  try {
+    decodeURIComponent(pathOnly);
+  } catch {
+    res.status(400).send('Bad Request: Invalid URL encoding');
+    return;
+  }
+  next();
+});
+
   // Set request-specific values in the very first middleware.
   app.use('/{*splat}', (req, res, next) => {
     setLatestRes(res);
diff --git a/test/integration/http.ts b/test/integration/http.ts
index ec78d4f9..b1087e3d 100644
--- a/test/integration/http.ts
+++ b/test/integration/http.ts
@@ -100,6 +100,14 @@ describe('HTTP Function', () => {
       expectedStatus: 404,
       expectedCallCount: 0,
     },
+    {
+      name: 'GET with non UTF-8 encoded chars',
+      httpVerb: 'GET',
+      path: '/%C3',
+      expectedBody: {},
+      expectedStatus: 400,
+      expectedCallCount: 0,
+    },
   ];
 
   testData.forEach(test => {