Index: generic/nsf.h
===================================================================
diff -u -rb604626384c5692394df7e276ac9c10e6229dbfd -rec5702daf07d4f8ed37deb09198ebff5b3fbb1bf
--- generic/nsf.h	(.../nsf.h)	(revision b604626384c5692394df7e276ac9c10e6229dbfd)
+++ generic/nsf.h	(.../nsf.h)	(revision ec5702daf07d4f8ed37deb09198ebff5b3fbb1bf)
@@ -398,6 +398,13 @@
 # define NSF_attribute_format(ARGS)
 #endif
 
+#if __GNUC_PREREQ(7, 0)
+# define NSF_FALL_THROUGH __attribute__((fallthrough))
+#else
+# define NSF_FALL_THROUGH ((void)0)
+#endif
+
+
 EXTERN int
 NsfArgumentError(Tcl_Interp *interp, const char *errorMsg, Nsf_Param const *paramPtr,
 		 Tcl_Obj *cmdNameObj, Tcl_Obj *methodPathObj)