diff --git a/cpp/s2psimh/s2psimh_core.cpp b/cpp/s2psimh/s2psimh_core.cpp
index 7f85592d..e0643d8e 100644
--- a/cpp/s2psimh/s2psimh_core.cpp
+++ b/cpp/s2psimh/s2psimh_core.cpp
@@ -154,7 +154,7 @@ int S2pSimh::Run(span<char*> args)
         return EXIT_SUCCESS;
     }
 
-    simh_file.open(simh_filename, ios::in | ios::out | ios::binary);
+    simh_file.open(simh_filename, (meta_data.empty() ? ios::in : ios::out) | ios::binary);
     if (simh_file.fail()) {
         cerr << "Error: Can't open '" << simh_filename << "':" << strerror(errno) << endl;
         return EXIT_FAILURE;