diff --git a/io/io/test/TFileTests.cxx b/io/io/test/TFileTests.cxx
index 647869e1d6b6a..a834eaeb5c8bc 100644
--- a/io/io/test/TFileTests.cxx
+++ b/io/io/test/TFileTests.cxx
@@ -141,6 +141,7 @@ TEST(TFile, k630forwardCompatibility)
 {
    gEnv->SetValue("TFile.v630forwardCompatibility", 1);
    const std::string filename{"filek30.root"};
+   // Testing that the flag is also set when creating the file from scratch (as opposed to "UPDATE")
    TFile filec{filename.c_str(),"RECREATE"};
    ASSERT_EQ(filec.TestBit(TFile::k630forwardCompatibility), true);  
    filec.Close();