diff --git a/runtests.sh b/runtests.sh
index 2a6c0ba47fa..837aab2ee1d 100755
--- a/runtests.sh
+++ b/runtests.sh
@@ -13,6 +13,7 @@ unset PYTHONPATH
 # Choose the Python binary.
 case `uname` in
 Darwin) PYTHON=./python.exe;;
+CYGWIN*) PYTHON=./python.exe;;
 *)      PYTHON=./python;;
 esac