diff --git a/test/prepare-build.sh b/test/prepare-build.sh
index 7c72006..bcc8c67 100755
--- a/test/prepare-build.sh
+++ b/test/prepare-build.sh
@@ -5,5 +5,8 @@ set -e
 rm -rf ~/.macstrap/macstrap.cfg
 cp ~/.macstrap/test/macstrap-test.cfg ~/.macstrap/macstrap.cfg
 
+# Uninstall preinstalled brew packages from Travis CI
+brew uninstall postgis postgresql
+
 # Start with the installation
 macstrap install