diff --git a/Modules/Setup.in b/Modules/Setup.in
index 9a1a4000c12..8f9c12be606 100644
--- a/Modules/Setup.in
+++ b/Modules/Setup.in
@@ -1,3 +1,4 @@
+# -*- makefile -*-
 # The file Setup is used by the makesetup script to construct the files
 # Makefile and config.c, from Makefile.pre and config.c.in,
 # respectively.  The file Setup itself is initially copied from