diff --git a/src/peek.c b/src/peek.c
index 54f010e..c84a2f8 100644
--- a/src/peek.c
+++ b/src/peek.c
@@ -17,6 +17,7 @@
  */
 
 #include <signal.h> /* sigaction(2), signal(2), struct sigaction, SIGINT */
+#include <stdbool.h> /* bool */
 #include <stdio.h> /* fprintf(3), fgetc(3), perror(3), fputc(3), stderr, stdin,
                     * stdout, EOF, NULL */
 #include <stdlib.h> /* exit(3), EXIT_FAILURE */
@@ -70,7 +71,7 @@ int main(int argc, char *argv[]){
 #endif
 
 	if (argc > 0) { /* option parsing */
-		char allow_nonterminals;
+		bool allow_nonterminals;
 		int c;
 
 		program_name = argv[0];