diff --git a/Makefile.inc1 b/Makefile.inc1
index 4039db00e709..6cd8cd771d24 100644
--- a/Makefile.inc1
+++ b/Makefile.inc1
@@ -229,7 +229,7 @@ USRDIRS=	usr/bin usr/lib/compat/aout usr/games usr/libdata/ldscripts \
 		usr/share/groff_font/devutf8 \
 		usr/share/tmac/mdoc usr/share/tmac/mm
 
-INCDIRS=	arpa g++/std objc protocols readline rpc rpcsvc openssl \
+INCDIRS=	arpa g++/std isc objc protocols readline rpc rpcsvc openssl \
 		security ss
 
 #