Index: generic/nsf.c
===================================================================
diff -u -r3ca38510f53a474fb940864c114952e73ce73e4b -rd223988ae01faec5a4ff14874d5db074e3c096b6
--- generic/nsf.c	(.../nsf.c)	(revision 3ca38510f53a474fb940864c114952e73ce73e4b)
+++ generic/nsf.c	(.../nsf.c)	(revision d223988ae01faec5a4ff14874d5db074e3c096b6)
@@ -15864,10 +15864,11 @@
       return NsfPrintError(interp,
                            "parameter option 'arg=' only allowed for user-defined converter");
     }
+
     if (paramPtr->converterArg != NULL) {
       DECR_REF_COUNT(paramPtr->converterArg);
     }
-
+    paramPtr->converterArg = Tcl_NewStringObj(option + 4, (int)optionLength - 4);
     /*
      * In case, we know that we have to unescape double commas, do it here...
      */