diff --git a/errors/invalid-route-source.md b/errors/invalid-route-source.md
new file mode 100644
index 000000000..fe2f40914
--- /dev/null
+++ b/errors/invalid-route-source.md
@@ -0,0 +1,33 @@
+# Invalid Custom Route `source`
+
+#### Why This Error Occurred
+
+When defining custom routes a route was added that causes an error during parsing. This can be due to trying to use normal `RegExp` syntax like negative lookaheads (`?!exclude`) without following `path-to-regexp`'s syntax for it.
+
+#### Possible Ways to Fix It
+
+Wrap the `RegExp` part of your `source` as an un-named parameter.
+
+**Before**
+
+```js
+{
+  source: '/feedback/(?!general)',
+  destination: '/feedback/general'
+}
+```
+
+**After**
+
+```js
+{
+  source: '/feedback/((?!general).*)',
+  destination: '/feedback/general'
+}
+```
+
+### Useful Links
+
+- [path-to-regexp](https://github.com/pillarjs/path-to-regexp/tree/v6.1.0)
+- [named parameters](https://github.com/pillarjs/path-to-regexp/blob/v6.1.0/Readme.md#named-parameters)
+- [un-named paramters](https://github.com/pillarjs/path-to-regexp/blob/v6.1.0/Readme.md#unnamed-parameters)
diff --git a/packages/now-routing-utils/src/index.ts b/packages/now-routing-utils/src/index.ts
index f7aefc1b2..7139f0775 100644
--- a/packages/now-routing-utils/src/index.ts
+++ b/packages/now-routing-utils/src/index.ts
@@ -14,6 +14,7 @@ import {
   convertRedirects,
   convertHeaders,
   convertTrailingSlash,
+  sourceToRegex,
 } from './superstatic';
 
 export { getCleanUrls } from './superstatic';
@@ -142,6 +143,18 @@ function checkRegexSyntax(src: string): NowErrorNested | null {
   return null;
 }
 
+function checkPatternSyntax(src: string): NowErrorNested | null {
+  try {
+    sourceToRegex(src);
+  } catch (err) {
+    return {
+      message: `Invalid pattern: "${src}"`,
+      src,
+    };
+  }
+  return null;
+}
+
 function createNowError(
   code: string,
   msg: string,
@@ -231,16 +244,29 @@ export function getTransformedRoutes({
 
   if (typeof redirects !== 'undefined') {
     const code = 'invalid_redirects';
-    const errors = redirects
+    const errorsRegex = redirects
       .map(r => checkRegexSyntax(r.source))
       .filter(notEmpty);
-    if (errors.length > 0) {
+    if (errorsRegex.length > 0) {
       return {
         routes,
         error: createNowError(
           code,
-          'Redirect `source` contains invalid regex',
-          errors
+          'Redirect `source` contains invalid regex. Read more: https://err.sh/now/invalid-route-source',
+          errorsRegex
+        ),
+      };
+    }
+    const errorsPattern = redirects
+      .map(r => checkPatternSyntax(r.source))
+      .filter(notEmpty);
+    if (errorsPattern.length > 0) {
+      return {
+        routes,
+        error: createNowError(
+          code,
+          'Redirect `source` contains invalid pattern. Read more: https://err.sh/now/invalid-route-source',
+          errorsPattern
         ),
       };
     }
@@ -265,16 +291,29 @@ export function getTransformedRoutes({
 
   if (typeof rewrites !== 'undefined') {
     const code = 'invalid_rewrites';
-    const errors = rewrites
+    const errorsRegex = rewrites
       .map(r => checkRegexSyntax(r.source))
       .filter(notEmpty);
-    if (errors.length > 0) {
+    if (errorsRegex.length > 0) {
       return {
         routes,
         error: createNowError(
           code,
-          'Rewrites `source` contains invalid regex',
-          errors
+          'Rewrites `source` contains invalid regex. Read more: https://err.sh/now/invalid-route-source',
+          errorsRegex
+        ),
+      };
+    }
+    const errorsPattern = rewrites
+      .map(r => checkPatternSyntax(r.source))
+      .filter(notEmpty);
+    if (errorsPattern.length > 0) {
+      return {
+        routes,
+        error: createNowError(
+          code,
+          'Rewrites `source` contains invalid pattern. Read more: https://err.sh/now/invalid-route-source',
+          errorsPattern
         ),
       };
     }
diff --git a/packages/now-routing-utils/src/superstatic.ts b/packages/now-routing-utils/src/superstatic.ts
index d0f3add5b..84613fc21 100644
--- a/packages/now-routing-utils/src/superstatic.ts
+++ b/packages/now-routing-utils/src/superstatic.ts
@@ -101,7 +101,9 @@ export function convertTrailingSlash(enable: boolean, status = 308): Route[] {
   return routes;
 }
 
-function sourceToRegex(source: string): { src: string; segments: string[] } {
+export function sourceToRegex(
+  source: string
+): { src: string; segments: string[] } {
   const keys: Key[] = [];
   const r = pathToRegexp(source, keys, { strict: true });
   const segments = keys.map(k => k.name).filter(isString);
diff --git a/packages/now-routing-utils/test/index.spec.js b/packages/now-routing-utils/test/index.spec.js
index d0f25d2fb..6a8c51d3a 100644
--- a/packages/now-routing-utils/test/index.spec.js
+++ b/packages/now-routing-utils/test/index.spec.js
@@ -568,6 +568,15 @@ describe('getTransformedRoutes', () => {
     assert.equal(actual.error.code, 'invalid_redirects');
   });
 
+  test('should error when redirects is invalid pattern', () => {
+    const nowConfig = {
+      redirects: [{ source: '/:?', destination: '/file.html' }],
+    };
+    const actual = getTransformedRoutes({ nowConfig });
+    assert.notEqual(actual.error, null);
+    assert.equal(actual.error.code, 'invalid_redirects');
+  });
+
   test('should error when rewrites is invalid regex', () => {
     const nowConfig = {
       rewrites: [{ source: '^/(*.)\\.html$', destination: '/file.html' }],
@@ -577,6 +586,15 @@ describe('getTransformedRoutes', () => {
     assert.equal(actual.error.code, 'invalid_rewrites');
   });
 
+  test('should error when rewrites is invalid pattern', () => {
+    const nowConfig = {
+      rewrites: [{ source: '/:?', destination: '/file.html' }],
+    };
+    const actual = getTransformedRoutes({ nowConfig });
+    assert.notEqual(actual.error, null);
+    assert.equal(actual.error.code, 'invalid_rewrites');
+  });
+
   test('should normalize all redirects before rewrites', () => {
     const nowConfig = {
       cleanUrls: true,