diff --git a/share/mk/bsd.dep.mk b/share/mk/bsd.dep.mk
index c371171512f9..117ea2ab6fc8 100644
--- a/share/mk/bsd.dep.mk
+++ b/share/mk/bsd.dep.mk
@@ -86,7 +86,7 @@ _SKIP_READ_DEPEND=	1
 CLEANFILES?=
 
 .for _S in ${SRCS:N*.[dhly]}
-OBJS_DEPEND_GUESS.${_S:R}.o=	${_S}
+OBJS_DEPEND_GUESS.${_S:R}.o+=	${_S}
 .endfor
 
 # Lexical analyzers
@@ -94,7 +94,7 @@ OBJS_DEPEND_GUESS.${_S:R}.o=	${_S}
 .for _LC in ${_LSRC:R}.c
 ${_LC}: ${_LSRC}
 	${LEX} ${LFLAGS} -o${.TARGET} ${.ALLSRC}
-OBJS_DEPEND_GUESS.${_LC:R}.o=	${_LC}
+OBJS_DEPEND_GUESS.${_LC:R}.o+=	${_LC}
 SRCS:=	${SRCS:S/${_LSRC}/${_LC}/}
 CLEANFILES+= ${_LC}
 .endfor
@@ -125,7 +125,7 @@ CLEANFILES+= ${_YH}
 ${_YC}: ${_YSRC}
 	${YACC} ${YFLAGS} -o ${_YC} ${.ALLSRC}
 .endif
-OBJS_DEPEND_GUESS.${_YC:R}.o=	${_YC}
+OBJS_DEPEND_GUESS.${_YC:R}.o+=	${_YC}
 .endfor
 .endfor
 
diff --git a/share/mk/bsd.lib.mk b/share/mk/bsd.lib.mk
index 0b7bb0230abd..ffb03c020ff6 100644
--- a/share/mk/bsd.lib.mk
+++ b/share/mk/bsd.lib.mk
@@ -424,13 +424,13 @@ lint: ${SRCS:M*.c}
 .if defined(LIB) && !empty(LIB)
 OBJS_DEPEND_GUESS+= ${SRCS:M*.h}
 .for _S in ${SRCS:N*.[hly]}
-OBJS_DEPEND_GUESS.${_S:R}.po=	${_S}
+OBJS_DEPEND_GUESS.${_S:R}.po+=	${_S}
 .endfor
 .endif
 .if defined(SHLIB_NAME) || \
     defined(INSTALL_PIC_ARCHIVE) && defined(LIB) && !empty(LIB)
 .for _S in ${SRCS:N*.[hly]}
-OBJS_DEPEND_GUESS.${_S:R}.So=	${_S}
+OBJS_DEPEND_GUESS.${_S:R}.So+=	${_S}
 .endfor
 .endif