diff --git a/src/lib/isCreditCard.js b/src/lib/isCreditCard.js
index 938679d39..950c8c30c 100644
--- a/src/lib/isCreditCard.js
+++ b/src/lib/isCreditCard.js
@@ -6,7 +6,7 @@ const cards = {
   dinersclub: /^3(?:0[0-5]|[68][0-9])[0-9]{11}$/,
   discover: /^6(?:011|5[0-9][0-9])[0-9]{12,15}$/,
   jcb: /^(?:2131|1800|35\d{3})\d{11}$/,
-  mastercard: /^5[1-5][0-9]{2}|(222[1-9]|22[3-9][0-9]|2[3-6][0-9]{2}|27[01][0-9]|2720)[0-9]{12}$/, // /^[25][1-7][0-9]{14}$/;
+  mastercard: /^(?:5[1-5][0-9]{14}|(222[1-9]|22[3-9][0-9]|2[3-6][0-9]{2}|27[01][0-9]|2720)[0-9]{12})$/,
   unionpay: /^(6[27][0-9]{14}|^(81[0-9]{14,17}))$/,
   visa: /^(?:4[0-9]{12})(?:[0-9]{3,6})?$/,
 };
diff --git a/test/validators.test.js b/test/validators.test.js
index 98d2a12ff..e4e88b01b 100644
--- a/test/validators.test.js
+++ b/test/validators.test.js
@@ -6635,6 +6635,34 @@ describe('Validators', () => {
   });
 
 
+  it('should reject short and partial Mastercard numbers (#2717)', () => {
+    // The Mastercard pattern's unanchored alternation (`^5[1-5][0-9]{2}|...`)
+    // used to match any 51-55 prefix regardless of length (#2717).
+    test({
+      validator: 'isCreditCard',
+      valid: [
+        '5105105105105100',
+        '5398228707871527',
+      ],
+      invalid: [
+        '5108',
+        '5108 5108 5108 5108 5108',
+      ],
+    });
+    test({
+      validator: 'isCreditCard',
+      args: [{ provider: 'mastercard' }],
+      valid: [
+        '5105105105105100',
+      ],
+      invalid: [
+        '5108',
+        '5108 5108 5108 5108 5108',
+      ],
+    });
+  });
+
+
   it('should validate Union Pay provided credit cards', () => {
     test({
       validator: 'isCreditCard',