Index: generic/nsfInt.h
===================================================================
diff -u -rb8ca306282c9a1000b1c93ffd97f7f4673953f65 -r295ac11031c89a0e649ea8b0ba3da8b6aa1ce953
--- generic/nsfInt.h	(.../nsfInt.h)	(revision b8ca306282c9a1000b1c93ffd97f7f4673953f65)
+++ generic/nsfInt.h	(.../nsfInt.h)	(revision 295ac11031c89a0e649ea8b0ba3da8b6aa1ce953)
@@ -1285,4 +1285,11 @@
 #endif
 #endif
 
+/* In Tcl 8.6 (tclInt.h), vsnprintf is mapped to _vsnprintf. In Tcl
+   8.5, this is missing from tclInt.h. So ... */ 
+
+#if defined(PRE86) && defined(_MSC_VER)
+#define vsnprintf _vsnprintf
+#endif
+
 #endif /* _nsf_int_h_ */