diff --git a/index.compiler.spec.js b/index.compiler.spec.js
index e85b5045..f4f252b4 100644
--- a/index.compiler.spec.js
+++ b/index.compiler.spec.js
@@ -802,6 +802,8 @@ describe('links', () => {
   });
 
   it('should sanitize links containing JS expressions', () => {
+    jest.spyOn(console, 'warn').mockImplementation(() => {});
+
     render(compiler('[foo](javascript:doSomethingBad)'));
 
     expect(root.innerHTML).toMatchInlineSnapshot(`
@@ -811,9 +813,45 @@ describe('links', () => {
 </a>
 
 `);
+
+    expect(console.warn).toHaveBeenCalled();
+  });
+
+  it('should sanitize links containing encoded JS expressions', () => {
+    jest.spyOn(console, 'warn').mockImplementation(() => {});
+
+    render(compiler('[foo](javascript%3AdoSomethingBad)'));
+
+    expect(root.innerHTML).toMatchInlineSnapshot(`
+
+<a data-reactroot>
+  foo
+</a>
+
+`);
+
+    expect(console.warn).toHaveBeenCalled();
+  });
+
+  it('should sanitize links containing padded JS expressions', () => {
+    jest.spyOn(console, 'warn').mockImplementation(() => {});
+
+    render(compiler('[foo](  javascript%3AdoSomethingBad)'));
+
+    expect(root.innerHTML).toMatchInlineSnapshot(`
+
+<a data-reactroot>
+  foo
+</a>
+
+`);
+
+    expect(console.warn).toHaveBeenCalled();
   });
 
   it('should sanitize links containing invalid characters', () => {
+    jest.spyOn(console, 'warn').mockImplementation(() => {});
+
     render(compiler('[foo](https://google.com/%AF)'));
 
     expect(root.innerHTML).toMatchInlineSnapshot(`
@@ -823,6 +861,7 @@ describe('links', () => {
 </a>
 
 `);
+    expect(console.warn).toHaveBeenCalled();
   });
 
   it('should handle a link with a URL in the text', () => {
diff --git a/index.js b/index.js
index ee7b4ac6..0bb196b4 100644
--- a/index.js
+++ b/index.js
@@ -604,14 +604,26 @@ function reactFor(outputFunc) {
 
 function sanitizeUrl(url) {
   try {
-    const prot = decodeURIComponent(url)
-      .replace(/[^A-Z0-9/:]/gi, '')
-      .toLowerCase();
+    const decoded = decodeURIComponent(url);
+
+    if (decoded.match(/^\s*javascript:/i)) {
+      if (process.env.NODE_ENV !== 'production') {
+        console.warn(
+          'Anchor URL contains an unsafe JavaScript expression, it will not be rendered.',
+          decoded
+        );
+      }
 
-    if (prot.indexOf('javascript:') === 0) {
       return null;
     }
   } catch (e) {
+    if (process.env.NODE_ENV !== 'production') {
+      console.warn(
+        'Anchor URL could not be decoded due to malformed syntax or characters, it will not be rendered.',
+        url
+      );
+    }
+
     // decodeURIComponent sometimes throws a URIError
     // See `decodeURIComponent('a%AFc');`
     // http://stackoverflow.com/questions/9064536/javascript-decodeuricomponent-malformed-uri-exception
@@ -667,6 +679,7 @@ function parseCaptureInline(capture, parse, state) {
 function captureNothing() {
   return {};
 }
+
 function renderNothing() {
   return null;
 }
@@ -677,11 +690,8 @@ function ruleOutput(rules) {
   };
 }
 
-function cx() {
-  return Array.prototype.slice
-    .call(arguments)
-    .filter(Boolean)
-    .join(' ');
+function cx(...args) {
+  return args.filter(Boolean).join(' ');
 }
 
 function get(src, path, fb) {