diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..ccc7596
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,6 @@
+*~
+*.o
+*.dpu
+*.exe
+dpu
+undpu
diff --git a/dpu.c b/dpu.c
index aa6fc80..5746339 100755
--- a/dpu.c
+++ b/dpu.c
@@ -7,7 +7,13 @@ int main (int argc, char **argv){
 	FILE *bob,*joe,*moe;
 	int thing, factor, arg;
 	if(argc >= 3){
-		factor = atoi (argv[1]);
+		char *end_char;
+		factor = strtol(argv[1], &end_char, 0);
+		if(!*(argv[1]) || *end_char)
+		{
+			fputs("I can haz number?\n", stderr);
+			return EXIT_FAILURE;
+		}
 		arg = 2;
 	}else{
 		factor = 9;