Index: generic/nsfError.c
===================================================================
diff -u -r4f4484003442910068436109bae0336b285476a3 -r34e5bc1b7adfbdd47a74590045b8b1310373a760
--- generic/nsfError.c	(.../nsfError.c)	(revision 4f4484003442910068436109bae0336b285476a3)
+++ generic/nsfError.c	(.../nsfError.c)	(revision 34e5bc1b7adfbdd47a74590045b8b1310373a760)
@@ -148,13 +148,19 @@
     
     va_copy(vargsCopy, vargs);
     result = vsnprintf(dsPtr->string + offset, avail, fmt, vargsCopy);
+    va_end(vargsCopy);
+    
 #if defined(_MSC_VER)
-    assert(result > -1);
+    failure = (result == -1);
 #else
-    assert(result > -1); /* no encoding error */
-    assert(result < avail); /* no overflow */
+    failure = (result == -1 || result >= avail);
 #endif
-    va_end(vargsCopy);
+
+    assert(failure == 0);
+    
+    if (unlikely(failure != 0)) {
+      fprintf(stderr, "copying variable argument vector into dynamic string failed\n");
+    }
   }
 }