diff --git a/tests/runtests.sh b/tests/runtests.sh
index 5b6113e..cae1f11 100755
--- a/tests/runtests.sh
+++ b/tests/runtests.sh
@@ -51,6 +51,7 @@ fi
 
 # for cygwin
 test -f ../cygchicken-0.dll && cp ../cygchicken-0.dll .
+mv ../cygchicken-0.dll ../cygchicken-0.dll_
 
 compile="../csc -compiler $CHICKEN -v -I.. -L.. -include-path .. -o a.out"
 compile2="../csc -compiler $CHICKEN -v -I.. -L.. -include-path .."