diff --git a/panda/src/downloadertools/check_md5.cxx b/panda/src/downloadertools/check_md5.cxx
index 27c33fa357..1bbc5855da 100644
--- a/panda/src/downloadertools/check_md5.cxx
+++ b/panda/src/downloadertools/check_md5.cxx
@@ -90,7 +90,7 @@ main(int argc, char **argv) {
       break;
 
     case 'b':
-      binary_output_filename = Filename::binary_filename(optarg);
+      binary_output_filename = Filename::binary_filename(string(optarg));
       break;
 
     case 'q':