diff --git a/tools/tools/nanobsd/defaults.sh b/tools/tools/nanobsd/defaults.sh
--- a/tools/tools/nanobsd/defaults.sh
+++ b/tools/tools/nanobsd/defaults.sh
@@ -884,7 +884,7 @@
 # Call this function to set defaults _after_ parsing options.
 # dont want a subshell otherwise variable setting is thrown away.
 set_defaults_and_export ( ) {
-	: ${NANO_OBJ:=/usr/obj/nanobsd.${NANO_NAME}${NANO_LAYOUT}:+.${NANO_LAYOUT}}
+	: ${NANO_OBJ:=/usr/obj/nanobsd.${NANO_NAME}${NANO_LAYOUT:+.${NANO_LAYOUT}}}
 	: ${MAKEOBJDIRPREFIX:=${NANO_OBJ}}
 	: ${NANO_DISKIMGDIR:=${NANO_OBJ}}
 	: ${NANO_WORLDDIR:=${NANO_OBJ}/_.w}