Index: sys/conf/kern.pre.mk
===================================================================
--- sys/conf/kern.pre.mk
+++ sys/conf/kern.pre.mk
@@ -208,6 +208,7 @@
 # Calculate path for .m files early, if needed.
 .if !defined(_MPATH)
 __MPATH!=find ${S:tA}/ -name \*_if.m
+_MFILES=${__MPATH:T:O}
 _MPATH=${__MPATH:H:O:u}
 .endif
 
@@ -227,7 +228,7 @@
 .if defined(DEBUG)
 MKMODULESENV+=	DEBUG_FLAGS="${DEBUG}"
 .endif
-MKMODULESENV+=	_MPATH="${_MPATH}"
+MKMODULESENV+=	_MPATH="${_MPATH}" _MFILES="${_MFILES}"
 
 # Architecture and output format arguments for objdump to convert image to
 # object file
Index: sys/conf/kmod.mk
===================================================================
--- sys/conf/kmod.mk
+++ sys/conf/kmod.mk
@@ -372,12 +372,16 @@
 # Build _if.[ch] from _if.m, and clean them when we're done.
 .if !defined(_MPATH)
 __MPATH!=find ${SYSDIR:tA}/ -name \*_if.m
+_MFILES=${__MPATH:T:O}
 _MPATH=${__MPATH:H:O:u}
 .endif
 .PATH.m: ${_MPATH}
 .for _i in ${SRCS:M*_if.[ch]}
-#removes too much, comment out until it's more constrained.
-#CLEANFILES+=	${_i}
+_MATCH=M${_i:R:S/$/.m/}
+_MATCHES=${_MFILES:${_MATCH}}
+.if !empty(_MATCHES)
+CLEANFILES+=	${_i}
+.endif
 .endfor # _i
 .m.c:	${SYSDIR}/tools/makeobjops.awk
 	${AWK} -f ${SYSDIR}/tools/makeobjops.awk ${.IMPSRC} -c