diff --git a/builds/libraries/vendor/libffi b/builds/libraries/vendor/libffi
index f189fa06c6258a4c0ad9386fe171222032b441ca..bfe7e38a8b89dfcd4b772b0cbc0a8315ce740683 100755
--- a/builds/libraries/vendor/libffi
+++ b/builds/libraries/vendor/libffi
@@ -4,7 +4,7 @@
 OUT_PREFIX=$1
 
 # Skip the build for heroku-16.
-if [[ S3_PREFIX == "heroku-16" ]]; then
+if [[ $S3_PREFIX == "heroku-16" ]]; then
     exit 0
 fi
 
diff --git a/builds/libraries/vendor/libmemcache b/builds/libraries/vendor/libmemcache
index a5b716f03420ae2a8dbcbe895745bf8e445c39a7..05c31318db3c4dc7e43f860b6d6e6b084bdc2f6d 100755
--- a/builds/libraries/vendor/libmemcache
+++ b/builds/libraries/vendor/libmemcache
@@ -4,7 +4,7 @@
 OUT_PREFIX=$1
 
 # Skip the build for heroku-16.
-if [[ S3_PREFIX == "heroku-16" ]]; then
+if [[ $S3_PREFIX == "heroku-16" ]]; then
     exit 0
 fi