diff --git a/include/boost/weak_ptr.hpp b/include/boost/weak_ptr.hpp
index d3a01fe..624cded 100644
--- a/include/boost/weak_ptr.hpp
+++ b/include/boost/weak_ptr.hpp
@@ -135,12 +135,12 @@ public:
 
     operator bool_type() const // never throws
     {
-        return use_count() == 0? 0: &this_type::use_count;
+        return px == 0 || use_count() == 0? 0: &this_type::use_count;
     }
 
     bool operator! () const // never throws
     {
-        return use_count() == 0;
+        return px == 0 || use_count() == 0;
     }
 
     void swap(this_type & other) // never throws
diff --git a/shared_ptr_test.cpp b/shared_ptr_test.cpp
index b5f80ed..749d8ee 100644
--- a/shared_ptr_test.cpp
+++ b/shared_ptr_test.cpp
@@ -249,6 +249,8 @@ int test_main(int, char * [])
         test_eq(wp2, wp4);
 
         wp1 = p2;
+        test_is_zero(wp1);
+
         wp1 = p4;
         wp1 = wp3;
         wp1 = wp2;