diff --git a/src/main.c b/src/main.c
index 8bff1ef..126413a 100644
--- a/src/main.c
+++ b/src/main.c
@@ -58,7 +58,7 @@ int main(int argc, char* argv[])
 
 	size_t input_len = strlen(argv[1]);
 	if (!(13 == input_len || 10 == input_len)) {
-		fprintf(stderr, "Invalid ISBN submitted!");
+		fprintf(stderr, "Invalid ISBN submitted!\n");
 		return EXIT_FAILURE;
 	}