1 files changed, 3 insertions, 2 deletions
diff --git a/src/output.c b/src/output.c
index 6d24b65..1d51a08 100644
--- a/src/output.c
+++ b/src/output.c
@@ -3,6 +3,7 @@
 #include <math.h>
 #include <stdio.h>
 #include <string.h>
+#include <errno.h>
 
 #include "output.h"
 
@@ -58,10 +59,10 @@ int scan_gas(gas_t *gas, char *str)
     }
 
     if (o2 < 0 || he < 0)
-        return -1;
+        return -EINVAL;
 
     if (o2 + he > 100)
-        return -1;
+        return -EINVAL;
 
     *gas = gas_new(o2, he, MOD_AUTO);
     return 0;