diff --git a/mxqsub.c b/mxqsub.c
index 07322e61..9e3c2dff 100644
--- a/mxqsub.c
+++ b/mxqsub.c
@@ -72,9 +72,8 @@ static void print_usage(void)
     "  -j, --threads=NUMBER     set number of threads       (default: 1)\n"
     "  -m, --memory=SIZE        set amount of memory        (default: 2G)\n"
     "\n"
-    "        [SIZE] may be suffixed with a combination of T, G and M\n"
-    "               to specify tebibytes, gibibytes and mebibytes.\n"
-    "               Defaults to mebibytes if no suffix is set.\n"
+    "        [SIZE] To specify megabytes, gigabytes or terrabytes,\n"
+    "               size must be suffixed with a unit (M, G or T).\n"
     "\n"
     "  -t, --runtime=TIME       set runtime                 (default: 15m)\n"
     "\n"
@@ -846,6 +845,9 @@ int main(int argc, char *argv[])
                         exit(EX_CONFIG);
                     }
                     arg_memory = bytes/1024/1024;
+                } else {
+                  mx_log_crit("--memory '%s': Size must have a unit (M, G, T).", optctl.optarg);
+                  exit(EX_CONFIG);
                 }
                 break;