diff --git a/include/boost/smart_ptr/detail/operator_bool.hpp b/include/boost/smart_ptr/detail/operator_bool.hpp
deleted file mode 100644
index dca171b..0000000
--- a/include/boost/smart_ptr/detail/operator_bool.hpp
+++ /dev/null
@@ -1,18 +0,0 @@
-//  This header intentionally has no include guards.
-//
-//  Copyright (c) 2001-2009, 2012 Peter Dimov
-//
-//  Distributed under the Boost Software License, Version 1.0.
-//  See accompanying file LICENSE_1_0.txt or copy at
-//  http://www.boost.org/LICENSE_1_0.txt
-
-    explicit operator bool () const BOOST_SP_NOEXCEPT
-    {
-        return px != 0;
-    }
-
-    // operator! is redundant, but some compilers need it
-    bool operator! () const BOOST_SP_NOEXCEPT
-    {
-        return px == 0;
-    }
diff --git a/include/boost/smart_ptr/intrusive_ptr.hpp b/include/boost/smart_ptr/intrusive_ptr.hpp
index ac181f2..278b8ea 100644
--- a/include/boost/smart_ptr/intrusive_ptr.hpp
+++ b/include/boost/smart_ptr/intrusive_ptr.hpp
@@ -163,8 +163,10 @@ public:
         return px;
     }
 
-// implicit conversion to "bool"
-#include <boost/smart_ptr/detail/operator_bool.hpp>
+    explicit operator bool () const BOOST_SP_NOEXCEPT
+    {
+        return px != 0;
+    }
 
     void swap(intrusive_ptr & rhs) BOOST_SP_NOEXCEPT
     {
diff --git a/include/boost/smart_ptr/local_shared_ptr.hpp b/include/boost/smart_ptr/local_shared_ptr.hpp
index bf011ef..0675c13 100644
--- a/include/boost/smart_ptr/local_shared_ptr.hpp
+++ b/include/boost/smart_ptr/local_shared_ptr.hpp
@@ -386,8 +386,10 @@ public:
         return px;
     }
 
-    // implicit conversion to "bool"
-#include <boost/smart_ptr/detail/operator_bool.hpp>
+    explicit operator bool () const BOOST_SP_NOEXCEPT
+    {
+        return px != 0;
+    }
 
     long local_use_count() const BOOST_SP_NOEXCEPT
     {
diff --git a/include/boost/smart_ptr/scoped_array.hpp b/include/boost/smart_ptr/scoped_array.hpp
index 43bee79..aa38bfa 100644
--- a/include/boost/smart_ptr/scoped_array.hpp
+++ b/include/boost/smart_ptr/scoped_array.hpp
@@ -85,8 +85,10 @@ public:
         return px;
     }
 
-// implicit conversion to "bool"
-#include <boost/smart_ptr/detail/operator_bool.hpp>
+    explicit operator bool () const BOOST_SP_NOEXCEPT
+    {
+        return px != 0;
+    }
 
     void swap(scoped_array & b) BOOST_SP_NOEXCEPT
     {
diff --git a/include/boost/smart_ptr/scoped_ptr.hpp b/include/boost/smart_ptr/scoped_ptr.hpp
index 1909496..148d6ec 100644
--- a/include/boost/smart_ptr/scoped_ptr.hpp
+++ b/include/boost/smart_ptr/scoped_ptr.hpp
@@ -111,8 +111,10 @@ public:
         return px;
     }
 
-// implicit conversion to "bool"
-#include <boost/smart_ptr/detail/operator_bool.hpp>
+    explicit operator bool () const BOOST_SP_NOEXCEPT
+    {
+        return px != 0;
+    }
 
     void swap(scoped_ptr & b) BOOST_SP_NOEXCEPT
     {
diff --git a/include/boost/smart_ptr/shared_array.hpp b/include/boost/smart_ptr/shared_array.hpp
index 2c28fad..24ac89b 100644
--- a/include/boost/smart_ptr/shared_array.hpp
+++ b/include/boost/smart_ptr/shared_array.hpp
@@ -176,8 +176,10 @@ public:
         return px;
     }
 
-// implicit conversion to "bool"
-#include <boost/smart_ptr/detail/operator_bool.hpp>
+    explicit operator bool () const BOOST_SP_NOEXCEPT
+    {
+        return px != 0;
+    }
 
     bool unique() const BOOST_SP_NOEXCEPT
     {
diff --git a/include/boost/smart_ptr/shared_ptr.hpp b/include/boost/smart_ptr/shared_ptr.hpp
index bcf27aa..4f5dbb4 100644
--- a/include/boost/smart_ptr/shared_ptr.hpp
+++ b/include/boost/smart_ptr/shared_ptr.hpp
@@ -581,8 +581,10 @@ public:
         return px;
     }
 
-// implicit conversion to "bool"
-#include <boost/smart_ptr/detail/operator_bool.hpp>
+    explicit operator bool () const BOOST_SP_NOEXCEPT
+    {
+        return px != 0;
+    }
 
     bool unique() const BOOST_SP_NOEXCEPT
     {