diff --git a/src/amo/middleware/prefixMiddleware.js b/src/amo/middleware/prefixMiddleware.js
index 3fdfcfd0fd8..911343c2416 100644
--- a/src/amo/middleware/prefixMiddleware.js
+++ b/src/amo/middleware/prefixMiddleware.js
@@ -28,6 +28,7 @@ export function prefixMiddleware(req, res, next, { _config = config } = {}) {
     lang: URLPathParts[0],
     acceptLanguage,
   });
+  let hasUnknownPartOne = false;
 
   const hasValidLang = isValidLang(URLPathParts[0]);
   const hasValidClientAppInPartOne = isValidClientApp(URLPathParts[0], {
@@ -58,9 +59,11 @@ export function prefixMiddleware(req, res, next, { _config = config } = {}) {
     hasValidClientAppUrlExceptionInPartTwo
   ) {
     log.debug(`Replacing lang in URL: ${URLPathParts[0]} with ${lang}`);
+    hasUnknownPartOne = true;
     URLPathParts.splice(0, 1, lang);
   } else {
     log.debug(`Prepending lang and clientApp to URL: ${lang}/${userAgentApp}`);
+    hasUnknownPartOne = !!URLPathParts[0];
     URLPathParts.splice(0, 0, lang, userAgentApp);
     isApplicationFromHeader = true;
   }
@@ -104,7 +107,10 @@ export function prefixMiddleware(req, res, next, { _config = config } = {}) {
       res.vary('user-agent');
     }
     res.set('Cache-Control', [`max-age=${ONE_YEAR_IN_SECONDS}`]);
-    return res.redirect(301, newURL);
+    // If there was something at the beginning of the URL we didn't recognize,
+    // it could be an old locale we have since disabled and might re-enable
+    // later, so make the redirect temporary (302), otherwise permanent (301).
+    return res.redirect(hasUnknownPartOne ? 302 : 301, newURL);
   }
 
   // Add the data to res.locals to be utilised later.
diff --git a/tests/unit/amo/middleware/test_prefixMiddleware.js b/tests/unit/amo/middleware/test_prefixMiddleware.js
index 33d6f890d5b..8efab3e5b0c 100644
--- a/tests/unit/amo/middleware/test_prefixMiddleware.js
+++ b/tests/unit/amo/middleware/test_prefixMiddleware.js
@@ -32,7 +32,7 @@ describe(__filename, () => {
       headers: {},
     };
     prefixMiddleware(fakeReq, fakeRes, fakeNext, { _config: fakeConfig });
-    sinon.assert.calledWith(fakeRes.redirect, 301, '/en-US/firefox');
+    sinon.assert.calledWith(fakeRes.redirect, 302, '/en-US/firefox');
     sinon.assert.calledWith(fakeRes.set, 'Cache-Control', ['max-age=31536000']);
     sinon.assert.notCalled(fakeNext);
   });
@@ -43,7 +43,7 @@ describe(__filename, () => {
       headers: {},
     };
     prefixMiddleware(fakeReq, fakeRes, fakeNext, { _config: fakeConfig });
-    sinon.assert.calledWith(fakeRes.redirect, 301, '/en-US/firefox');
+    sinon.assert.calledWith(fakeRes.redirect, 302, '/en-US/firefox');
     sinon.assert.calledWith(fakeRes.set, 'Cache-Control', ['max-age=31536000']);
     sinon.assert.notCalled(fakeNext);
   });
@@ -77,7 +77,7 @@ describe(__filename, () => {
     prefixMiddleware(fakeReq, fakeRes, fakeNext, { _config: fakeConfig });
     sinon.assert.calledWith(
       fakeRes.redirect,
-      301,
+      302,
       '/en-US/validprefix/whatever',
     );
     sinon.assert.calledWith(fakeRes.set, 'Cache-Control', ['max-age=31536000']);
@@ -90,7 +90,7 @@ describe(__filename, () => {
       headers: {},
     };
     prefixMiddleware(fakeReq, fakeRes, fakeNext, { _config: fakeConfig });
-    sinon.assert.calledWith(fakeRes.redirect, 301, '/en-US/developers/');
+    sinon.assert.calledWith(fakeRes.redirect, 302, '/en-US/developers/');
     sinon.assert.calledWith(fakeRes.set, 'Cache-Control', ['max-age=31536000']);
     sinon.assert.calledWith(fakeRes.vary, 'accept-language');
   });
@@ -114,7 +114,7 @@ describe(__filename, () => {
       headers: {},
     };
     prefixMiddleware(fakeReq, fakeRes, fakeNext, { _config: fakeConfig });
-    sinon.assert.calledWith(fakeRes.redirect, 301, '/pt-PT/firefox/whatever');
+    sinon.assert.calledWith(fakeRes.redirect, 302, '/pt-PT/firefox/whatever');
     sinon.assert.calledWith(fakeRes.set, 'Cache-Control', ['max-age=31536000']);
   });
 
@@ -126,7 +126,7 @@ describe(__filename, () => {
       },
     };
     prefixMiddleware(fakeReq, fakeRes, fakeNext, { _config: fakeConfig });
-    sinon.assert.calledWith(fakeRes.redirect, 301, '/pt-BR/firefox/whatever');
+    sinon.assert.calledWith(fakeRes.redirect, 302, '/pt-BR/firefox/whatever');
     sinon.assert.calledWith(fakeRes.vary, 'accept-language');
     sinon.assert.calledWith(fakeRes.vary, 'user-agent');
     sinon.assert.calledWith(fakeRes.set, 'Cache-Control', ['max-age=31536000']);
@@ -218,7 +218,7 @@ describe(__filename, () => {
     prefixMiddleware(fakeReq, fakeRes, fakeNext, { _config: fakeConfig });
     sinon.assert.calledWith(
       fakeRes.redirect,
-      301,
+      302,
       '/en-US/firefox/foo/bar?test=1&bar=2',
     );
     sinon.assert.calledWith(fakeRes.set, 'Cache-Control', ['max-age=31536000']);