diff --git a/src/oxframe.c b/src/oxframe.c
index 00dd9e7..37ef91b 100644
--- a/src/oxframe.c
+++ b/src/oxframe.c
@@ -67,7 +67,7 @@ typedef struct _oxstate {
 
 static void usage(void){
   fprintf(stderr,
-          "Usage: oxframe [options]\n\n"
+          "Usage: oxframe -i <input> -o <output> [options]\n\n"
           "Options: \n\n"
           "  -h, --help            show this help message and exit\n"
           "  -x WIDTH, --width=WIDTH\n"
@@ -538,7 +538,7 @@ int main (int argc, char * argv[]) {
     }
   }
 
-  if(argc < 3) {
+  if(argc < 3 || state.input == NULL || state.output == NULL) {
     usage();
   }