diff --git a/Makefile b/Makefile
index cd5a04a..a20b18f 100644
--- a/Makefile
+++ b/Makefile
@@ -6,7 +6,7 @@ TARGET = slr
 PREFIX ?= /usr/local
 BINDIR = $(PREFIX)/bin
 
-CFLAGS = -O3 -march=native -mtune=native -pipe -s -std=c99 -pedantic -Wall
+CFLAGS = -Os -march=native -mtune=native -pipe -s -std=c99 -pedantic -Wall -D_DEFAULT_SOURCE
 
 SRC = slr.c lexer.c parser.c
 
diff --git a/lexer.c b/lexer.c
index c21f340..cbc0e07 100644
--- a/lexer.c
+++ b/lexer.c
@@ -39,7 +39,7 @@ Token *lexer(char *buf)
         current_index++;
     }
     tokens[tokens_index].type = END_OF_TOKENS;
-    tokens[tokens_index].value = '\0';
+    tokens[tokens_index].value = NULL;
     return tokens;
 }