diff --git a/cmd_parser.c b/cmd_parser.c
index 3eb4986..f976fe2 100644
--- a/cmd_parser.c
+++ b/cmd_parser.c
@@ -62,12 +62,13 @@ inline uint8_t isletter(uint8_t l)
 {
 	// return (l >= 'a' && l <= 'z') || (l >= 'A' && l <= 'Z');
 
-	// Make it upper case
+	// Make it lowercase
 	l |= 0x20;
-	l -= 'A';
-	return (l <= ('Z'-'A'));
+	l -= 'a';
+	return (l <= ('z'-'a'));
 }
 
+
 inline uint8_t isnumber(uint8_t l)
 {
 	// return (l >= '0' && l <= '9');