diff --git a/Library/Homebrew/cmd/vendor-install.sh b/Library/Homebrew/cmd/vendor-install.sh
index 8f08e49fb0..9ab004ee87 100644
--- a/Library/Homebrew/cmd/vendor-install.sh
+++ b/Library/Homebrew/cmd/vendor-install.sh
@@ -76,10 +76,10 @@ fetch() {
     trap - SIGINT
   fi
 
-  if [[ -n "$(which shasum)" ]]
+  if [[ -x "$(which shasum)" ]]
   then
     sha="$(shasum -a 256 "$CACHED_LOCATION" | cut -d' ' -f1)"
-  elif [[ -n "$(which sha256sum)" ]]
+  elif [[ -x "$(which sha256sum)" ]]
   then
     sha="$(sha256sum "$CACHED_LOCATION" | cut -d' ' -f1)"
   else