diff --git a/package/jimtcl/jimtcl.mk b/package/jimtcl/jimtcl.mk
index 313970d94a..68c8a914db 100644
--- a/package/jimtcl/jimtcl.mk
+++ b/package/jimtcl/jimtcl.mk
@@ -38,6 +38,12 @@ define JIMTCL_INSTALL_LIB
 endef
 endif
 
+# build system doesn't use autotools, but does use an old version of
+# gnuconfig which doesn't know all the architectures supported by
+# Buildroot, so update config.guess / config.sub like we do in
+# pkg-autotools.mk
+JIMTCL_POST_PATCH_HOOKS += UPDATE_CONFIG_HOOK
+
 define JIMTCL_CONFIGURE_CMDS
 	(cd $(@D); \
 		$(TARGET_CONFIGURE_OPTS) CCACHE=none \