diff --git a/builds/msvc/properties/Common.props b/builds/msvc/properties/Common.props
index e1af65cac..1b31d765d 100644
--- a/builds/msvc/properties/Common.props
+++ b/builds/msvc/properties/Common.props
@@ -27,7 +27,7 @@
 
       <!-- Language -->
       <!-- /Zc is conformance mode. -->
-      <AdditionalOptions>/Zc:__cplusplus %(AdditionalOptions)</AdditionalOptions>
+      <AdditionalOptions>/Zc:__cplusplus /Zc:preprocessor %(AdditionalOptions)</AdditionalOptions>
       <EnforceTypeConversionRules>true</EnforceTypeConversionRules>
       <RuntimeTypeInfo>true</RuntimeTypeInfo>
       <OpenMPSupport>false</OpenMPSupport>
diff --git a/src/protocols/protocol_explore.cpp b/src/protocols/protocol_explore.cpp
index 016b7fe79..87fbca278 100644
--- a/src/protocols/protocol_explore.cpp
+++ b/src/protocols/protocol_explore.cpp
@@ -76,6 +76,7 @@ bool protocol_explore::try_dispatch_object(const request& request) NOEXCEPT
 
     const auto& query = archive();
     const auto wit = params["witness"] != "false";
+    constexpr auto header_size = chain::header::serialized_size();
 
     if (is_json)
     {
@@ -83,7 +84,7 @@ bool protocol_explore::try_dispatch_object(const request& request) NOEXCEPT
         {
             if (const auto ptr = query.get_header(query.to_header(hash)))
             {
-                send_json(request, value_from(ptr), ptr->serialized_size());
+                send_json(request, value_from(ptr), header_size);
                 return true;
             }
         }