diff --git a/src/lib/isHSL.js b/src/lib/isHSL.js
index 05cb43962..05d8d3ec2 100644
--- a/src/lib/isHSL.js
+++ b/src/lib/isHSL.js
@@ -2,7 +2,7 @@ import assertString from './util/assertString';
 
 
 const hslComma = /^hsla?\(((\+|\-)?([0-9]+(\.[0-9]+)?(e(\+|\-)?[0-9]+)?|\.[0-9]+(e(\+|\-)?[0-9]+)?))(deg|grad|rad|turn)?(,(\+|\-)?([0-9]+(\.[0-9]+)?(e(\+|\-)?[0-9]+)?|\.[0-9]+(e(\+|\-)?[0-9]+)?)%){2}(,((\+|\-)?([0-9]+(\.[0-9]+)?(e(\+|\-)?[0-9]+)?|\.[0-9]+(e(\+|\-)?[0-9]+)?)%?))?\)$/i;
-const hslSpace = /^hsla?\(((\+|\-)?([0-9]+(\.[0-9]+)?(e(\+|\-)?[0-9]+)?|\.[0-9]+(e(\+|\-)?[0-9]+)?))(deg|grad|rad|turn)?(\s(\+|\-)?([0-9]+(\.[0-9]+)?(e(\+|\-)?[0-9]+)?|\.[0-9]+(e(\+|\-)?[0-9]+)?)%){2}\s?(\/\s((\+|\-)?([0-9]+(\.[0-9]+)?(e(\+|\-)?[0-9]+)?|\.[0-9]+(e(\+|\-)?[0-9]+)?)%?)\s?)?\)$/i;
+const hslSpace = /^hsla?\(((\+|\-)?([0-9]+(\.[0-9]+)?(e(\+|\-)?[0-9]+)?|\.[0-9]+(e(\+|\-)?[0-9]+)?))(deg|grad|rad|turn)?(\s(\+|\-)?([0-9]+(\.[0-9]+)?(e(\+|\-)?[0-9]+)?|\.[0-9]+(e(\+|\-)?[0-9]+)?)%){2}\s?(\/\s?((\+|\-)?([0-9]+(\.[0-9]+)?(e(\+|\-)?[0-9]+)?|\.[0-9]+(e(\+|\-)?[0-9]+)?)%?)\s?)?\)$/i;
 
 
 export default function isHSL(str) {
diff --git a/test/validators.test.js b/test/validators.test.js
index 98d2a12ff..3d6207167 100644
--- a/test/validators.test.js
+++ b/test/validators.test.js
@@ -5108,6 +5108,31 @@ describe('Validators', () => {
     });
   });
 
+  it('should allow optional whitespace around the HSL alpha separator', () => {
+    test({
+      validator: 'isHSL',
+      valid: [
+        'hsl(120 100% 50%/0.5)',
+        'hsl(120 100% 50% /0.5)',
+        'hsl(120 100% 50%/ 0.5)',
+        'hsl(120 100% 50% / 0.5)',
+        'hsla(120 100% 50%/50%)',
+        'hsla(120 100% 50% /50%)',
+        'hsla(120 100% 50%/ 50%)',
+        'hsla(120 100% 50% / 50%)',
+        'hsl(120 100% 50%/.5)',
+        'hsl(120 100% 50%\t/\t0.5)',
+      ],
+      invalid: [
+        'hsl(120 100% 50%/)',
+        'hsl(120 100% 50%/ )',
+        'hsl(120 100% 50%//0.5)',
+        'hsl(120 100% 50%/0. 5)',
+        'hsl(120 100% 50%/50 %)',
+      ],
+    });
+  });
+
   it('should validate rgb color strings', () => {
     test({
       validator: 'isRgbColor',