diff --git a/samples/condor/boinc_gahp.cpp b/samples/condor/boinc_gahp.cpp
index d499944d21..df02c04623 100644
--- a/samples/condor/boinc_gahp.cpp
+++ b/samples/condor/boinc_gahp.cpp
@@ -459,7 +459,7 @@ void handle_fetch_output(COMMAND& c) {
         } else {
             sprintf(path, "%s/%s", req.dir, req.stderr_filename.c_str());
         }
-        FILE* f = fopen(path, "w");
+        FILE* f = fopen(path, "a");
         if (!f) {
             sprintf(buf, "can't\\ open\\ stderr\\ output\\ file\\ %s ", path);
             s = string(buf);