diff --git a/include/boost/detail/lightweight_test.hpp b/include/boost/detail/lightweight_test.hpp
index 8c4fc33..33f5234 100644
--- a/include/boost/detail/lightweight_test.hpp
+++ b/include/boost/detail/lightweight_test.hpp
@@ -1,8 +1,8 @@
 #ifndef BOOST_DETAIL_LIGHTWEIGHT_TEST_HPP_INCLUDED
 #define BOOST_DETAIL_LIGHTWEIGHT_TEST_HPP_INCLUDED
 
-#if _MSC_VER >= 1020
-#pragma once
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
 #endif
 
 //
diff --git a/include/boost/detail/quick_allocator.hpp b/include/boost/detail/quick_allocator.hpp
index 58cc1d8..83987d5 100644
--- a/include/boost/detail/quick_allocator.hpp
+++ b/include/boost/detail/quick_allocator.hpp
@@ -1,8 +1,8 @@
 #ifndef BOOST_DETAIL_QUICK_ALLOCATOR_HPP_INCLUDED
 #define BOOST_DETAIL_QUICK_ALLOCATOR_HPP_INCLUDED
 
-#if _MSC_VER >= 1020
-#pragma once
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
 #endif
 
 //