diff --git a/src/opts.c b/src/opts.c
index 1d44c69..e32e44d 100644
--- a/src/opts.c
+++ b/src/opts.c
@@ -10,7 +10,7 @@ uint8_t getoptions(int32_t argc, char *const *argv, int32_t *ncpus) {
 	uint8_t opts = 0;
 	char opt;
 
-	while ((opt = getopt(argc, argv, "lavi")) != -1) {
+	while ((opt = getopt(argc, argv, "lavih")) != -1) {
 		switch (opt) {
 		case 'l':
 			if (opts & OPT_LIST_CORES) fatal("-%c has already been set", 'l');
@@ -29,7 +29,20 @@ uint8_t getoptions(int32_t argc, char *const *argv, int32_t *ncpus) {
 			opts |= OPT_INVERT;
 			break;
 		case '?':
-			fatal("usage: %s [number] [-l] [-a] [-v] [-i]", argv[0]);
+			printf("specify -h for help\n");
+			exit(EXIT_FAILURE);
+		case 'h':
+			printf(
+				"%s: a tool for turning on/off CPU threads\n"
+				"USAGE: %s [integer] [-l] [-a] [-v] [-i] [-h]\n"
+				"ARGUMENTS:\n"
+				"\t-l : List cores after executing the command. May be specified without integer.\n"
+				"\t-a : Writes to all cores, regardless of their state.\n"
+				"\t-v : Print the cores that are written. (implies -l)\n"
+				"\t-i : Instead of the given number.\n"
+				"\t-h : Shows this dialogue.\n",
+				argv[0], argv[0]);
+			exit(EXIT_SUCCESS);
 		}
 	}