diff --git a/examples/custom_rtti.cpp b/examples/custom_rtti.cpp
index cc8d2a5..6e43d7f 100644
--- a/examples/custom_rtti.cpp
+++ b/examples/custom_rtti.cpp
@@ -3,6 +3,10 @@
 // See accompanying file LICENSE_1_0.txt
 // or copy at http://www.boost.org/LICENSE_1_0.txt)
 
+#ifdef _MSC_VER
+#pragma warning(disable: 4312)
+#endif
+
 struct Animal {
     Animal(unsigned type) : type(type) {
     }
diff --git a/examples/deferred_custom_rtti.cpp b/examples/deferred_custom_rtti.cpp
index 2c9af72..d60c330 100644
--- a/examples/deferred_custom_rtti.cpp
+++ b/examples/deferred_custom_rtti.cpp
@@ -3,6 +3,10 @@
 // See accompanying file LICENSE_1_0.txt
 // or copy at http://www.boost.org/LICENSE_1_0.txt)
 
+#ifdef _MSC_VER
+#pragma warning(disable: 4312)
+#endif
+
 // tag::classes[]
 struct custom_type_info {
     static unsigned last;
diff --git a/include/boost/openmethod/compiler.hpp b/include/boost/openmethod/compiler.hpp
index 351ef30..464344d 100644
--- a/include/boost/openmethod/compiler.hpp
+++ b/include/boost/openmethod/compiler.hpp
@@ -95,7 +95,7 @@ struct generic_compiler {
         std::vector<parameter> used_by_vp;
         boost::dynamic_bitset<> used_slots;
         boost::dynamic_bitset<> reserved_slots;
-        int first_slot = 0;
+        std::size_t first_slot = 0;
         std::size_t mark = 0; // temporary mark to detect cycles
         std::vector<vtbl_entry> vtbl;
         vptr_type* static_vptr;
diff --git a/include/boost/openmethod/registry.hpp b/include/boost/openmethod/registry.hpp
index c073c8d..22e9c3a 100644
--- a/include/boost/openmethod/registry.hpp
+++ b/include/boost/openmethod/registry.hpp
@@ -6,6 +6,7 @@
 #include <boost/mp11/algorithm.hpp>
 #include <boost/mp11/bind.hpp>
 
+#include <stdlib.h>
 #include <vector>
 
 namespace boost::openmethod {
@@ -61,8 +62,18 @@ struct trace : policy {
     template<class Registry>
     struct fn {
         inline static bool trace_enabled = []() {
+#ifdef _MSC_VER
+            char* env;
+            std::size_t len;
+            auto result =
+                _dupenv_s(&env, &len, "BOOST_OPENMETHOD_TRACE") == 0 && env &&
+                len == 2 && *env == '1';
+            free(env);
+            return result;
+#else
             auto env = getenv("BOOST_OPENMETHOD_TRACE");
             return env && *env++ == '1' && *env++ == 0;
+#endif
         }();
     };
 };