diff --git a/pngpriv.h b/pngpriv.h
index 6d2e424d2..2369b8e29 100644
--- a/pngpriv.h
+++ b/pngpriv.h
@@ -466,7 +466,14 @@
    static_cast<type>(static_cast<const void*>(value))
 #else
 #  define png_voidcast(type, value) (value)
-#  define png_constcast(type, value) ((type)(value))
+#  if defined( _WIN64 ) && ! defined( __GNUC__ )
+      typedef unsigned __int64 png_ptruint;
+#  elif defined( _WIN64 )
+      typedef unsigned long long png_ptruint;
+#  else
+      typedef unsigned long png_ptruint;
+#  endif
+#  define png_constcast(type, value) ((type)(png_ptruint)(const void*)(value))
 #  define png_aligncast(type, value) ((void*)(value))
 #  define png_aligncastconst(type, value) ((const void*)(value))
 #endif /* __cplusplus */