diff --git a/phing/composer-install.sh b/phing/composer-install.sh
index 1a951a2..1d8d259 100644
--- a/phing/composer-install.sh
+++ b/phing/composer-install.sh
@@ -7,7 +7,7 @@ EXPECTED_SIGNATURE="$(curl -L https://composer.github.io/installer.sig)"
 php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
 ACTUAL_SIGNATURE="$(php -r "echo hash_file('SHA384', 'composer-setup.php');")"
 
-if [ "$EXPECTED_SIGNATURE" != "$ACTUAL_SIGNATURE" ]
+if [[ "$EXPECTED_SIGNATURE" != "$ACTUAL_SIGNATURE" ]]
 then
     >&2 echo 'ERROR: Invalid installer signature'
     rm composer-setup.php
@@ -17,4 +17,4 @@ fi
 php composer-setup.php --quiet
 RESULT=$?
 rm composer-setup.php
-exit $RESULT
+exit ${RESULT}