diff --git a/util/mk1mf.pl b/util/mk1mf.pl
index cbf845ae7..324871f62 100755
--- a/util/mk1mf.pl
+++ b/util/mk1mf.pl
@@ -404,6 +404,11 @@ for (;;)
 	}
 close(IN);
 
+# Remove opensslconf.h so it doesn't get updated if we configure a
+# different branch.
+$exheader =~ s/[^ ]+\/opensslconf.h//;
+$header =~ s/[^ ]+\/opensslconf.h//;
+
 if ($shlib)
 	{
 	$extra_install= <<"EOF";
@@ -581,6 +586,7 @@ $banner
 # This needs to be invoked once, when the makefile is first constructed, or
 # after cleaning.
 init: \$(TMP_D) \$(LIB_D) \$(INC_D) \$(INCO_D) \$(BIN_D) \$(TEST_D) headers
+	\$(PERL) \$(SRC_D)/util/copy-if-different.pl "\$(SRC_D)/crypto/opensslconf.h" "\$(INCO_D)/opensslconf.h"
 
 headers: \$(HEADER) \$(EXHEADER)