diff --git a/tools/jfjoch_hdf5_test.cpp b/tools/jfjoch_hdf5_test.cpp
index 295eb35a..7457ce55 100644
--- a/tools/jfjoch_hdf5_test.cpp
+++ b/tools/jfjoch_hdf5_test.cpp
@@ -69,8 +69,11 @@ int main(int argc, char **argv) {
     else
         x.FilePrefix(std::getenv("HDF5DATASET_WRITE_TEST_PREFIX"));
 
-    std::cout << "Using new format for HDF5 master file" << std::endl;
-    x.SetFileWriterFormat(FileWriterFormat::NXmxVDS);
+    if (std::getenv("HDF5MASTER_NEW_FORMAT") != nullptr) {
+        std::cout << "Using new format for HDF5 master file" << std::endl;
+        x.SetFileWriterFormat(FileWriterFormat::NXmxVDS);
+    } else
+        x.SetFileWriterFormat(FileWriterFormat::NXmxLegacy);
 
     x.ImagesPerTrigger(nimages);