diff --git a/README.md b/README.md
index 34e4603..8f24a50 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 # C JSON Parser
 
 Just a simple project to practice writing parsers.
-Not guaranteed to be safe or efficient.
+Not guaranteed to be safe, reliable or efficient.
 
 ## Usage
 
@@ -16,7 +16,7 @@ To make a debug build just run `make`.
 ### Run
 
 ```sh
-./bin/{release|debug}/json_parser
+./bin/{release|debug}/json_parser sample.json
 ```
 
 ## Limitations
diff --git a/src/main.c b/src/main.c
index 16efdf4..9896bf4 100644
--- a/src/main.c
+++ b/src/main.c
@@ -4,13 +4,17 @@
 #include "util.h"
 
 #include <stdlib.h> // atexit
-#include <unistd.h> // _exit
+#include <err.h> // errx
 
-int main()
+int main(int argc, char* argv[])
 {
+	if (argc != 2) {
+		errx(EXIT_FAILURE, "Usage: %s <file>", argv[0]);
+	}
+
     atexit(print_trace);
 
-    FILE* fp = fopen("sample.json", "r");
+    FILE* fp = fopen(argv[1], "r");
 
     volatile struct json_value x = parse_json_value(fp);