diff --git a/project/config/cfgdefs.sh b/project/config/cfgdefs.sh
index 64d8dc1..02b19b3 100644
--- a/project/config/cfgdefs.sh
+++ b/project/config/cfgdefs.sh
@@ -160,7 +160,7 @@ cfgdefs_perform_common_tests()
 	cfgtest_makevar_append '-DNCURSES_INTERNALS'
 
 	# <panel.h>
-	if [ -n "$mb_panel_wrapper" ]; then
+	if [ _${mb_panel_wrapper:-} = _yes ]; then
 		cfgtest_makevar_append '-I$(PROJECT_DIR)/wrappers'
 		unset mb_panel_wrapper
 	fi