diff --git a/src/lib/isFloat.js b/src/lib/isFloat.js
index 84bdc782c..9fe2d602b 100644
--- a/src/lib/isFloat.js
+++ b/src/lib/isFloat.js
@@ -5,6 +5,9 @@ import { decimal } from './alpha';
 export default function isFloat(str, options) {
   assertString(str);
   options = options || {};
+  if (options.locale && !(options.locale in decimal)) {
+    throw new Error(`Invalid locale '${options.locale}'`);
+  }
   const float = new RegExp(`^(?:[-+])?(?:[0-9]+)?(?:\\${options.locale ? decimal[options.locale] : '.'}[0-9]*)?(?:[eE][\\+\\-]?(?:[0-9]+))?$`);
   if (str === '' || str === '.' || str === ',' || str === '-' || str === '+') {
     return false;
diff --git a/test/validators.test.js b/test/validators.test.js
index 98d2a12ff..60bf0e6ab 100644
--- a/test/validators.test.js
+++ b/test/validators.test.js
@@ -4940,6 +4940,19 @@ describe('Validators', () => {
     });
   });
 
+  it('should error on invalid locale', () => {
+    test({
+      validator: 'isFloat',
+      args: [{ locale: 'is-NOT' }],
+      error: [
+        '123',
+        '123.123',
+        '123,123',
+        '3undefined5',
+      ],
+    });
+  });
+
   it('should validate hexadecimal strings', () => {
     test({
       validator: 'isHexadecimal',