1 files changed, 6 insertions, 2 deletions
diff --git a/xbacklight.c b/xbacklight.c
index b7c8011..64a043d 100644
--- a/xbacklight.c
+++ b/xbacklight.c
@@ -64,9 +64,13 @@ static double
 atof_or_die (char *str)
 {
     double retval;
+    char *endptr = NULL;
     errno = 0;
-    retval = strtod(str, NULL);
-    if (errno) usage(1);
+    retval = strtod(str, &endptr);
+    if ((errno != 0) || (endptr == str)) {
+        fprintf(stderr, "%s: invalid argument '%s'\n", program_name, str);
+        usage(1);
+    }
     return retval;
 }