diff --git a/appveyor.yml b/appveyor.yml
index 2618f6943f9..c2efa7e7d04 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -37,6 +37,8 @@ cache:
 - win_flex_bison-2.4.5.zip
 - llvm-3.3.1-msvc2013-mtd.7z
 
+os: Visual Studio 2013
+
 environment:
   WINFLEXBISON_ARCHIVE: win_flex_bison-2.4.5.zip
   LLVM_ARCHIVE: llvm-3.3.1-msvc2013-mtd.7z