diff --git a/bin/yarn b/bin/yarn
index 4c71f7083..727c23f8e 100755
--- a/bin/yarn
+++ b/bin/yarn
@@ -12,7 +12,7 @@ command_exists() {
 }
 
 if command_exists node; then
-  if [ "$YARN_FORCE_WINPTY" -eq 1 ]; then
+  if [[ "$YARN_FORCE_WINPTY" -eq 1 ]]; then
     winpty node "$basedir/yarn.js" "$@"
   else
     node "$basedir/yarn.js" "$@"