diff --git a/Makefile.inc1 b/Makefile.inc1
index 28dc8fbfc4e5..65b0ebc0ab92 100644
--- a/Makefile.inc1
+++ b/Makefile.inc1
@@ -144,6 +144,15 @@ CLEANDIR=	clean cleandepend
 CLEANDIR=	cleandir
 .endif
 
+.if ${MK_META_MODE} == "yes"
+# If filemon is used then we can rely on the build being incremental-safe.
+# The .meta files will also track the build command and rebuild should
+# it change.
+.if empty(.MAKE.MODE:Mnofilemon)
+NO_CLEAN=	t
+.endif
+.endif
+
 LOCAL_TOOL_DIRS?=
 PACKAGEDIR?=	${DESTDIR}/${DISTDIR}
 
diff --git a/share/man/man7/build.7 b/share/man/man7/build.7
index 36603dac5ac3..a605c2846bd2 100644
--- a/share/man/man7/build.7
+++ b/share/man/man7/build.7
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd March 29, 2016
+.Dd April 14, 2016
 .Dt BUILD 7
 .Os
 .Sh NAME
@@ -539,6 +539,14 @@ instead of
 .Dq make cleandir .
 .It Va NO_CLEAN
 If set, no object tree files are cleaned at all.
+This is the default when
+.Va WITH_META_MODE
+is used with
+.Xr filemon 4
+loaded.
+See
+.Xr src.conf 5
+for more details.
 Setting
 .Va NO_CLEAN
 implies