Index: generic/nsf.c
===================================================================
diff -u -rf90a7fadfad292db51ef8f46fbd477bf82f2ee78 -rf4c0008af1841b4c67fd34cd6646df02f310e297
--- generic/nsf.c	(.../nsf.c)	(revision f90a7fadfad292db51ef8f46fbd477bf82f2ee78)
+++ generic/nsf.c	(.../nsf.c)	(revision f4c0008af1841b4c67fd34cd6646df02f310e297)
@@ -17503,6 +17503,12 @@
     /*
      * copy the remaining argument vector
      */
+
+#if defined(NDEBUG)
+    if (objv == NULL) {
+      assert(cscPtr->objv != NULL);
+    }
+#endif
     memcpy(nobjv + methodNameLength, objv == NULL ? cscPtr->objv : objv, sizeof(Tcl_Obj *) * objc);
 
     INCR_REF_COUNT(nobjv[0]); /* we seem to need this here */