diff --git a/project/config/cfgdefs.sh b/project/config/cfgdefs.sh
index 8b7ac20..245ba3f 100644
--- a/project/config/cfgdefs.sh
+++ b/project/config/cfgdefs.sh
@@ -134,6 +134,18 @@ cfgdefs_perform_target_tests()
 	mb_cfgtest_makevar='LDFLAGS_NCURSES_LIBS'
 	cfgtest_makevar_append $mb_ncurses_libs
 
+	# tcl/tk libc
+	for mb_tcltk_ver in 8.9 8.8 8.7 8.6 8.5; do
+		if [ -z "$mb_tcltk_libs" ]; then
+			mb_tcltk_libs="-ltk$mb_tcltk_ver -ltcl$mb_tcltk_ver"
+			cfgtest_library_presence $mb_tcltk_libs \
+				|| mb_tcltk_libs=''
+		fi
+	done
+
+	mb_cfgtest_makevar='LDFLAGS_TCLTK_LIBS'
+	cfgtest_makevar_append "$mb_tcltk_libs"
+
 	# pretty cfgdefs.mk
 	cfgtest_newline
 }