diff --git a/mxqsub.c b/mxqsub.c
index 5ee8cee..478886a 100644
--- a/mxqsub.c
+++ b/mxqsub.c
@@ -989,7 +989,10 @@ int main(int argc, char *argv[])
                 break;
 
             case 7:
-                {
+                u_int64_t  arg_tmpdir_mb;
+                if (mx_strtou64(optctl.optarg, &arg_tmpdir_mb) == 0) {
+                    arg_tmpdir = (arg_tmpdir_mb+1024-1)/1024;
+                } else {
                     unsigned long long int bytes;
                     if(mx_strtobytes(optctl.optarg, &bytes) < 0) {
                         mx_log_crit("--tmpdir '%s': %m", optctl.optarg);