diff --git a/num_enum/tests/from_primitive.rs b/num_enum/tests/from_primitive.rs
index 2c72c6c..d727db2 100644
--- a/num_enum/tests/from_primitive.rs
+++ b/num_enum/tests/from_primitive.rs
@@ -8,6 +8,26 @@ mod core {}
 mod num_enum {}
 mod std {}
 
+#[test]
+fn has_from_primitive_number_u64() {
+    #[derive(Debug, Eq, PartialEq, FromPrimitive)]
+    #[repr(u64)]
+    enum Enum {
+        Zero = 0,
+        #[num_enum(default)]
+        NonZero = 1,
+    }
+
+    let zero = Enum::from_primitive(0_u64);
+    assert_eq!(zero, Enum::Zero);
+
+    let one = Enum::from_primitive(1_u64);
+    assert_eq!(one, Enum::NonZero);
+
+    let two = Enum::from_primitive(2_u64);
+    assert_eq!(two, Enum::NonZero);
+}
+
 #[test]
 fn has_from_primitive_number() {
     #[derive(Debug, Eq, PartialEq, FromPrimitive)]
diff --git a/num_enum_derive/src/lib.rs b/num_enum_derive/src/lib.rs
index 8c77862..a7f8843 100644
--- a/num_enum_derive/src/lib.rs
+++ b/num_enum_derive/src/lib.rs
@@ -209,8 +209,9 @@ impl EnumInfo {
                 .strip_prefix('i')
                 .or_else(|| repr_str.strip_prefix('u'));
             if let Some(suffix) = suffix {
-                if let Ok(bits) = suffix.parse::<u8>() {
-                    return Ok(1 << bits == self.variants.len());
+                if let Ok(bits) = suffix.parse::<u32>() {
+                    let variants = 1usize.checked_shl(bits);
+                    return Ok(variants.map_or(false, |v| v == self.variants.len()));
                 }
             }
         }