diff --git a/ChangeLog b/ChangeLog
index 6ec6549b51..8b84a003ec 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Sun Nov 13 12:43:48 2011  Tanaka Akira  <akr@fsij.org>
+
+	* ext/dbm/extconf.rb: rollback $libs and $defs when db detection is
+	  failed.  It fixes -lgdbm -lqdbm when the system has qdbm and gdbm
+	  without gdbm_compat.
+
 Sat Nov 12 21:14:51 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* test/webrick/test_cgi.rb (class TestWEBrickCGI): respect
diff --git a/ext/dbm/extconf.rb b/ext/dbm/extconf.rb
index b46688aa75..f8139495d3 100644
--- a/ext/dbm/extconf.rb
+++ b/ext/dbm/extconf.rb
@@ -29,6 +29,17 @@ headers.found = []
 headers.defs = nil
 
 def headers.db_check(db)
+  old_libs = $libs
+  old_defs = $defs
+  result = db_check2(db)
+  if !result
+    $libs = old_libs
+    $defs = old_defs
+  end
+  result
+end
+
+def headers.db_check2(db)
   hsearch = nil
 
   case db