diff --git a/.travis.yml b/.travis.yml
index 6693243a2669dc1607fced21a20302f29296e919..ed190cd1628f47047b3b8a7c934aa1efdc2d2f23 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,7 +1,7 @@
 language: csharp
 solution: Compilers.sln
 mono:
- - latest
+ - 6.4.0
  
 install:
   - sudo apt-get install nunit-console