diff --git a/src/passes/1-parser/shared/Lexer.mll b/src/passes/1-parser/shared/Lexer.mll
index 2821acc85..8b213f70b 100644
--- a/src/passes/1-parser/shared/Lexer.mll
+++ b/src/passes/1-parser/shared/Lexer.mll
@@ -580,7 +580,7 @@ let letter     = small | capital
 let ident      = small (letter | '_' | digit)*
 let constr     = capital (letter | '_' | digit)*
 let attr       = ident | constr
-let hexa_digit = digit | ['A'-'F']
+let hexa_digit = digit | ['A'-'F' 'a'-'f']
 let byte       = hexa_digit hexa_digit
 let byte_seq   = byte | byte (byte | '_')* byte
 let bytes      = "0x" (byte_seq? as seq)