diff --git a/ext/dbm/extconf.rb b/ext/dbm/extconf.rb
index 5c6c183eac..2fc5c441a5 100644
--- a/ext/dbm/extconf.rb
+++ b/ext/dbm/extconf.rb
@@ -16,8 +16,8 @@ headers = {
   "db4" => ["db4/db.h", "db4.h", "db.h"],
   "db5" => ["db5/db.h", "db5.h", "db.h"],
   "dbm" => ["ndbm.h"],
-  "gdbm" => ["gdbm-ndbm.h", "ndbm.h", "gdbm/ndbm.h"],
-  "gdbm_compat" => ["gdbm-ndbm.h", "ndbm.h", "gdbm/ndbm.h"], # ndbm compatibility routines are extracted to libgdbm_compat since gdbm-1.8.1.
+  "gdbm" => ["gdbm-ndbm.h", "ndbm.h", "gdbm/ndbm.h"], # gdbm until 1.8.0
+  "gdbm_compat" => ["gdbm-ndbm.h", "ndbm.h", "gdbm/ndbm.h"], # gdbm since 1.8.1
   "qdbm" => ["relic.h", "qdbm/relic.h"],
 }