diff --git a/src/lib/datasrc/tests/memory/zone_writer_unittest.cc b/src/lib/datasrc/tests/memory/zone_writer_unittest.cc
index 52f8d242e7..bc9b103111 100644
--- a/src/lib/datasrc/tests/memory/zone_writer_unittest.cc
+++ b/src/lib/datasrc/tests/memory/zone_writer_unittest.cc
@@ -219,7 +219,7 @@ TEST_F(ZoneWriterLocalTest, retry) {
     const ZoneTable::FindResult found(table->findZone(Name("example.org")));
     ASSERT_EQ(isc::datasrc::result::SUCCESS, found.code);
     // For some reason it doesn't seem to work by the ZoneNode typedef, using
-    // the full definition instead.
+    // the full definition instead. At least on some compilers.
     const isc::datasrc::memory::DomainTreeNode<RdataSet>* node;
     EXPECT_EQ(isc::datasrc::memory::DomainTree<RdataSet>::EXACTMATCH,
               found.zone_data->getZoneTree().