--- boost\iostreams\detail\adapter\non_blocking_adapter.hpp	(current revision)
+++ boost\iostreams\detail\adapter\non_blocking_adapter.hpp	(working copy)
@@ -25,13 +25,14 @@
         { };
     explicit non_blocking_adapter(Device& dev) : device_(dev) { }
     std::streamsize read(char_type* s, std::streamsize n)
     { 
         std::streamsize result = 0;
         while (result < n) {
-            std::streamsize amt = iostreams::read(device_, s, n);
+            std::streamsize amt =
+              iostreams::read(device_, s + result, n - result);
             if (amt == -1)
                 break;
             result += amt;
         }
         return result != 0 ? result : -1;
     }