diff --git a/larky/src/main/resources/vendor/luhn.star b/larky/src/main/resources/vendor/luhn.star
index b66a79e53..13de65091 100644
--- a/larky/src/main/resources/vendor/luhn.star
+++ b/larky/src/main/resources/vendor/luhn.star
@@ -21,6 +21,8 @@ def verify(num):
     >>> verify('534618613411236')
     False
     """
+    if not isdigit(num):
+        return False
     checksum = int(num[-1])
     cardSum = int(_luhn_summation(num,-2))
     return ((cardSum + checksum) % 10) == 0
diff --git a/larky/src/test/resources/vendor_tests/luhn/luhn_test.star b/larky/src/test/resources/vendor_tests/luhn/luhn_test.star
index 4353d838f..94fa16fa0 100644
--- a/larky/src/test/resources/vendor_tests/luhn/luhn_test.star
+++ b/larky/src/test/resources/vendor_tests/luhn/luhn_test.star
@@ -8,6 +8,9 @@ def test_valid():
 def test_invalid():
     asserts.assert_that(luhn.verify('4222222222222222')).is_equal_to(False)
 
+def test_nonumeric():
+    asserts.assert_that(luhn.verify('422222222x22222')).is_equal_to(False)
+
 def test_generate():
     asserts.assert_that(luhn.generate('7992739871')).is_equal_to(3)