diff --git a/sys/modules/geom/geom_flashmap/Makefile b/sys/modules/geom/geom_flashmap/Makefile
index 8b56c145ea5..97e4fd7337b 100644
--- a/sys/modules/geom/geom_flashmap/Makefile
+++ b/sys/modules/geom/geom_flashmap/Makefile
@@ -5,4 +5,9 @@
 KMOD=	geom_flashmap
 SRCS=	geom_flashmap.c
 
+.if !empty(OPT_FDT)
+.PATH:	${SRCTOP}/sys/dev/fdt
+SRCS+=	fdt_slicer.c
+.endif
+
 .include <bsd.kmod.mk>