diff --git a/exercises/luhn/example.rs b/exercises/luhn/example.rs
index da6c35021..e2eb42421 100644
--- a/exercises/luhn/example.rs
+++ b/exercises/luhn/example.rs
@@ -1,5 +1,6 @@
 pub fn is_valid(candidate: &str) -> bool {
-    if candidate.chars().any(|c| c.is_alphabetic()) || candidate.chars().count() == 1 {
+    if candidate.chars().filter(|c| c.is_digit(10)).take(2).count() <= 1 ||
+       candidate.chars().any(|c| !c.is_digit(10) && c != ' ') {
         return false;
     }
 
diff --git a/exercises/luhn/tests/luhn.rs b/exercises/luhn/tests/luhn.rs
index bcf809e5e..7a400f3e5 100644
--- a/exercises/luhn/tests/luhn.rs
+++ b/exercises/luhn/tests/luhn.rs
@@ -13,6 +13,12 @@ fn single_zero_string_is_invalid() {
     assert!(!is_valid("0"));
 }
 
+#[test]
+#[ignore]
+fn simple_valid_sin() {
+    assert!(is_valid(" 5 9 "));
+}
+
 #[test]
 #[ignore]
 fn valid_canadian_sin_is_valid() {
@@ -36,3 +42,39 @@ fn invalid_credit_card_is_invalid() {
 fn strings_that_contain_non_digits_are_invalid() {
     assert!(!is_valid("046a 454 286"));
 }
+
+#[test]
+#[ignore]
+fn punctuation_is_invalid() {
+    assert!(!is_valid("055-444-285"));
+}
+
+#[test]
+#[ignore]
+fn symbols_are_invalid() {
+    assert!(!is_valid("055£ 444$ 285"));
+}
+
+#[test]
+#[ignore]
+fn single_digit_with_space_is_invalid() {
+    assert!(!is_valid(" 0"));
+}
+
+#[test]
+#[ignore]
+fn lots_of_zeros_are_valid() {
+    assert!(is_valid(" 00000"));
+}
+
+#[test]
+#[ignore]
+fn another_valid_sin() {
+    assert!(is_valid("055 444 285"));
+}
+
+#[test]
+#[ignore]
+fn nine_doubled_is_nine() {
+    assert!(is_valid("091"));
+}