diff --git a/travis/before_install-macos.sh b/travis/before_install-macos.sh
index e4f469c38..361e4b26c 100755
--- a/travis/before_install-macos.sh
+++ b/travis/before_install-macos.sh
@@ -5,6 +5,6 @@ set -euo pipefail
 thisdir=$(dirname "$0")
 
 brew update
-brew install python3
+brew install mono python3
 
 "$thisdir/before_install-common.sh"