diff --git a/appveyor.yml b/appveyor.yml
index 65a521370..576042cdf 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -1,9 +1,9 @@
 version: 1.0.{build}
-image: Visual Studio 2015
+image: Visual Studio 2017
 before_build:
 - md %APPVEYOR_BUILD_FOLDER%\build
 - cd %APPVEYOR_BUILD_FOLDER%\build
-- cmake -G "Visual Studio 14 Win64" -DOPTDBG=1 -DWITH_XPRESS=1 -DPORTABLE=1 ..
+- cmake -G "Visual Studio 15 Win64" -DOPTDBG=1 -DWITH_XPRESS=1 -DPORTABLE=1 ..
 - cd ..
 build:
   project: build\rocksdb.sln
diff --git a/db/external_sst_file_test.cc b/db/external_sst_file_test.cc
index 89e949ff0..8f7c86839 100644
--- a/db/external_sst_file_test.cc
+++ b/db/external_sst_file_test.cc
@@ -388,9 +388,10 @@ class SstFileWriterCollector : public TablePropertiesCollector {
   const char* Name() const override { return name_.c_str(); }
 
   Status Finish(UserCollectedProperties* properties) override {
+    std::string count = std::to_string(count_);
     *properties = UserCollectedProperties{
         {prefix_ + "_SstFileWriterCollector", "YES"},
-        {prefix_ + "_Count", std::to_string(count_)},
+        {prefix_ + "_Count", count},
     };
     return Status::OK();
   }