diff --git a/src/parser/macros.rs b/src/parser/macros.rs
index dfeb201b..326772cf 100644
--- a/src/parser/macros.rs
+++ b/src/parser/macros.rs
@@ -192,7 +192,7 @@ macro_rules! single_quote_char {
 #[macro_export]
 macro_rules! small_letter_char {
     ($c: expr) => {
-        $c.is_lowercase()
+        $c.is_alphabetic() && !$c.is_uppercase()
     };
 }