diff --git a/share/mk/bsd.dep.mk b/share/mk/bsd.dep.mk
--- a/share/mk/bsd.dep.mk
+++ b/share/mk/bsd.dep.mk
@@ -192,6 +192,17 @@
 # avoid collisions.
 DEPEND_FILTER=	C,/,_,g
 .if !empty(OBJS)
+.if !defined(_ALLOW_ABSOLUTE_OBJ_PATH) && ${OBJS:M/*}
+# Absolute paths to OBJS should be an error inside ${SRCTOP}, but some users
+# might be relying on this feature, so add an opt-out mechanism.
+.if defined(SRCTOP) && ${OBJS:M${SRCTOP}*}
+.error "$$OBJS inside $$SRCTOP not allowed: ${OBJS:M${SRCTOP}*}"
+.elif ${OBJS:N${_ABSOLUTE_PATH_OBJS}:M/*}
+.error "$$OBJS absolute path not allowed: ${OBJS:N${_ABSOLUTE_PATH_OBJS}:M/*}. \
+    If this is intended, add them to _ABSOLUTE_PATH_OBJS to silence this error\
+    or define _ALLOW_ABSOLUTE_OBJ_PATH to disable this diagnostic."
+.endif
+.endif
 DEPENDOBJS+=	${OBJS}
 .else
 DEPENDSRCS+=	${SRCS:M*.[cSC]} ${SRCS:M*.cxx} ${SRCS:M*.cpp} ${SRCS:M*.cc}