diff --git a/src/testdir/Makefile b/src/testdir/Makefile
index 65c82e0..8ae35b9 100644
--- a/src/testdir/Makefile
+++ b/src/testdir/Makefile
@@ -57,7 +57,7 @@
 
 RM_ON_RUN = test.out X* viminfo
 RM_ON_START = tiny.vim small.vim mbyte.vim mzscheme.vim lua.vim test.ok
-RUN_VIM = export VIMRUNTIME=$(SCRIPTSOURCE); $(VALGRIND) $(VIMPROG) -u unix.vim -U NONE --noplugin -s dotest.in
+RUN_VIM = VIMRUNTIME=$(SCRIPTSOURCE); export VIMRUNTIME; $(VALGRIND) $(VIMPROG) -u unix.vim -U NONE --noplugin -s dotest.in
 
 clean:
 	-rm -rf *.out *.failed *.rej *.orig test.log $(RM_ON_RUN) $(RM_ON_START) valgrind.*