Index: generic/nsfError.c
===================================================================
diff -u -r9149131f82853343544588c8667969e03a296397 -rce2d2c1c7d116762e09e8bc047491eb4c3db4808
--- generic/nsfError.c	(.../nsfError.c)	(revision 9149131f82853343544588c8667969e03a296397)
+++ generic/nsfError.c	(.../nsfError.c)	(revision ce2d2c1c7d116762e09e8bc047491eb4c3db4808)
@@ -78,11 +78,14 @@
 #endif
 
   if (failure) {
+    int addedStringLength;
 #ifdef _WIN32
     /* Compute the required size of the Tcl_DString */
-    int addedStringLength = _vscprintf(fmt, vargsCopy);
+    va_copy(vargsCopy, vargs);
+    addedStringLength = _vscprintf(fmt, vargsCopy);
+    va_end(vargsCopy);
 #else
-    int addedStringLength = result;
+    addedStringLength = result;
 #endif
     Tcl_DStringSetLength(dsPtr, offset + addedStringLength);