diff --git a/src/lib/isBase64.js b/src/lib/isBase64.js
index fd876e4c0..67e734e57 100644
--- a/src/lib/isBase64.js
+++ b/src/lib/isBase64.js
@@ -12,6 +12,7 @@ export default function isBase64(str, options) {
 
   if (str === '') return true;
 
+  if (str.length % 4 === 1) return false;
   if (options.padding && str.length % 4 !== 0) return false;
 
   let regex;
@@ -21,5 +22,5 @@ export default function isBase64(str, options) {
     regex = options.padding ? base64WithPadding : base64WithoutPadding;
   }
 
-  return (!options.padding || str.length % 4 === 0) && regex.test(str);
+  return regex.test(str);
 }
diff --git a/test/validators/isBase64.test.js b/test/validators/isBase64.test.js
index c0074343a..9bf30c5ae 100644
--- a/test/validators/isBase64.test.js
+++ b/test/validators/isBase64.test.js
@@ -26,6 +26,9 @@ describe('isBase64', () => {
         'HQIDAQAB',
       ],
       invalid: [
+        'A',
+        'AAAAA',
+        'AAAAAAAAA',
         '12345',
         'Vml2YW11cyBmZXJtZtesting123',
         'Zg=',