diff --git a/appveyor.yml b/appveyor.yml
index 0d85453e1..4f423e2f2 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -1,20 +1,26 @@
 version: '{build}'
 
-configuration:
-  - Debug
-  - Release
-
 os: 
   - Visual Studio 2015
   - Visual Studio 2017
 
+environment:
+  matrix:
+  - additional_flags: ""
+  - additional_flags: "/permissive- /std:c++latest /utf-8"
+
+matrix:
+  exclude:
+    - additional_flags: "/permissive- /std:c++latest /utf-8"
+      os: Visual Studio 2015
+  
 init: []
 
 install: []
 
 build_script:
   - IF "%APPVEYOR_BUILD_WORKER_IMAGE%" == "Visual Studio 2015" ( SET GEN="Visual Studio 14 2015") ELSE (SET GEN="Visual Studio 15 2017")
-  - cmake . -G%GEN% 
+  - cmake . -G%GEN% -DCMAKE_CXX_FLAGS="%additional_flags%"
   - cmake --build . --config Release
 
 test_script:
diff --git a/src/json.hpp b/src/json.hpp
index 98659054e..3b8925a3f 100644
--- a/src/json.hpp
+++ b/src/json.hpp
@@ -3729,6 +3729,9 @@ class basic_json
                    not std::is_same<ValueType, typename string_t::value_type>::value
 #ifndef _MSC_VER  // fix for issue #167 operator<< ambiguity under VS2015
                    and not std::is_same<ValueType, std::initializer_list<typename string_t::value_type>>::value
+#endif
+#if defined(_MSC_VER) && defined(_HAS_CXX17) && _HAS_CXX17 == 1 // fix for issue #464
+                   and not std::is_same<ValueType, typename std::string_view>::value
 #endif
                    , int >::type = 0 >
     operator ValueType() const
diff --git a/src/json.hpp.re2c b/src/json.hpp.re2c
index 5e90f611c..eca19ccff 100644
--- a/src/json.hpp.re2c
+++ b/src/json.hpp.re2c
@@ -3729,6 +3729,9 @@ class basic_json
                    not std::is_same<ValueType, typename string_t::value_type>::value
 #ifndef _MSC_VER  // fix for issue #167 operator<< ambiguity under VS2015
                    and not std::is_same<ValueType, std::initializer_list<typename string_t::value_type>>::value
+#endif
+#if defined(_MSC_VER) && defined(_HAS_CXX17) && _HAS_CXX17 == 1 // fix for issue #464
+                   and not std::is_same<ValueType, typename std::string_view>::value
 #endif
                    , int >::type = 0 >
     operator ValueType() const