diff --git a/1/GNUmakefile b/1/GNUmakefile
index 211f586..eed98a1 100644
--- a/1/GNUmakefile
+++ b/1/GNUmakefile
@@ -1,2 +1,2 @@
 # -*- makefile-gmake -*-
-include ../GNUmakefile.common
+include ../gnu.mk
diff --git a/1/makefile b/1/makefile
index 1191f1d..058141b 100644
--- a/1/makefile
+++ b/1/makefile
@@ -1,2 +1,2 @@
 # -*- makefile-bsdmake -*-
-.include "../makefile.common"
+.include "../common.mk"
diff --git a/makefile.common b/common.mk
similarity index 100%
rename from makefile.common
rename to common.mk
diff --git a/GNUmakefile.common b/gnu.mk
similarity index 100%
rename from GNUmakefile.common
rename to gnu.mk