diff --git a/src/lexer/lexer_utils.c b/src/lexer/lexer_utils.c
index 9883bf7..07455a7 100644
--- a/src/lexer/lexer_utils.c
+++ b/src/lexer/lexer_utils.c
@@ -60,34 +60,22 @@ static void set_token_keyword(struct token *tok, char *begin, ssize_t size)
 {
     if (tok->type != TOKEN_NULL || size == 0)
         return;
-    if (strncmp(begin, "if", size) == 0 && size == 2)
-    {
+    if (strncmp(begin, "!", size) == 0 && size == 1)
+        tok->type = TOKEN_NEGATION;
+    else if (strncmp(begin, "if", size) == 0 && size == 2)
         tok->type = TOKEN_IF;
-    }
     else if (strncmp(begin, "fi", size) == 0 && size == 2)
-    {
         tok->type = TOKEN_FI;
-    }
     else if (strncmp(begin, "then", size) == 0 && size == 4)
-    {
         tok->type = TOKEN_THEN;
-    }
     else if (strncmp(begin, "else", size) == 0 && size == 4)
-    {
         tok->type = TOKEN_ELSE;
-    }
     else if (strncmp(begin, "elif", size) == 0 && size == 4)
-    {
         tok->type = TOKEN_ELIF;
-    }
     else if (strncmp(begin, "&&", size) == 0 && size == 2)
-    {
         tok->type = TOKEN_AND;
-    }
     else if (strncmp(begin, "||", size) == 0 && size == 2)
-    {
         tok->type = TOKEN_OR;
-    }
 
     // no keywords found.
     if (tok->type == TOKEN_NULL)
@@ -95,7 +83,10 @@ static void set_token_keyword(struct token *tok, char *begin, ssize_t size)
 
     tok->data = calloc(size + 1, sizeof(char));
     if (tok->data == NULL)
+    {
+        perror("could not allocate memory in lexer");
         return;
+    }
     strncpy(tok->data, begin, size);
 }
 
diff --git a/src/lexer/lexer_utils.h b/src/lexer/lexer_utils.h
index 29d444d..6b26c74 100644
--- a/src/lexer/lexer_utils.h
+++ b/src/lexer/lexer_utils.h
@@ -49,7 +49,7 @@ enum token_type
     TOKEN_LEFT_BRACKET,
     TOKEN_RIGHT_BRACKET,
     TOKEN_PIPE,
-    TOKEN_NEGATION, // TODO handle
+    TOKEN_NEGATION,
 
     // TODO merge into one and use the data field
     // (Too difficult to handle in the parser because of firsts)