diff --git a/.appveyor.yml b/.appveyor.yml
index 2bf46ade..6711b614 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -9,7 +9,7 @@ install:
 
 build_script:
   - cd C:\projects\cquery
-  - python waf configure --msvc_version="msvc 14.0" --msvc_targets=x64
+  - python waf configure --msvc_version="msvc 15.0"
   - python waf build
   - ps: |
       $dir = "cquery-${env:appveyor_build_version}-win64"
@@ -26,7 +26,5 @@ artifacts:
   - path: 'cquery-*.zip'
 
 cache:
-  - C:\projects\cquery\build\LLVM-4.0.0-win64.exe
   - C:\projects\cquery\build\LLVM-5.0.1-win64.exe
-  - C:\projects\cquery\build\LLVM-4.0.0-win64\
   - C:\projects\cquery\build\LLVM-5.0.1-win64\
diff --git a/src/test.cc b/src/test.cc
index a4a544d1..bc18d05a 100644
--- a/src/test.cc
+++ b/src/test.cc
@@ -124,6 +124,8 @@ bool RunIndexTests(const std::string& filter_path, bool enable_update) {
 
   bool success = true;
   bool update_all = false;
+  // FIXME: show diagnostics in STL/headers when running tests. At the moment
+  // this can be done by constructing ClangIndex index(1, 1);
   ClangIndex index;
 
   for (std::string path : GetFilesInFolder("index_tests", true /*recursive*/,
@@ -152,8 +154,9 @@ bool RunIndexTests(const std::string& filter_path, bool enable_update) {
     bool had_extra_flags = !flags.empty();
     if (!AnyStartsWith(flags, "-x"))
       flags.push_back("-xc++");
+    // Use c++14 by default, because MSVC STL is written assuming that.
     if (!AnyStartsWith(flags, "-std"))
-      flags.push_back("-std=c++11");
+      flags.push_back("-std=c++14");
     flags.push_back("-resource-dir=" + GetDefaultResourceDirectory());
     if (had_extra_flags) {
       std::cout << "For " << path << std::endl;