diff --git a/posix.mak b/posix.mak
index 6126b8aa84e..32c11d0d2e3 100644
--- a/posix.mak
+++ b/posix.mak
@@ -138,7 +138,7 @@ endif
 
 # Set DFLAGS
 DFLAGS=
-override DFLAGS+=-conf= -I$(DRUNTIME_PATH)/import $(DMDEXTRAFLAGS) -w -de -preview=dip25 $(MODEL_FLAG) $(PIC) -transition=complex
+override DFLAGS+=-conf= -I$(DRUNTIME_PATH)/import $(DMDEXTRAFLAGS) -w -de -preview=dip1000 $(MODEL_FLAG) $(PIC) -transition=complex
 ifeq ($(BUILD),debug)
 override DFLAGS += -g -debug
 else
@@ -362,7 +362,7 @@ UT_D_OBJS:=$(addprefix $(ROOT)/unittest/,$(addsuffix $(DOTOBJ),$(D_MODULES)))
 $(UT_D_OBJS): $(ALL_D_FILES)
 $(UT_D_OBJS): $(ROOT)/unittest/%$(DOTOBJ): %.d
 	@mkdir -p $(dir $@)
-	$(DMD) $(DFLAGS) $(UDFLAGS) -preview=dip1000 -c -of$@ $<
+	$(DMD) $(DFLAGS) $(UDFLAGS) -c -of$@ $<
 
 ifneq (1,$(SHARED))
 
@@ -647,7 +647,7 @@ betterc: betterc-phobos-tests
 	@[ -f "$(TESTS_EXTRACTOR)" ] || ${MAKE} -f posix.mak "$(TESTS_EXTRACTOR)"
 	@$(TESTS_EXTRACTOR) --betterC --attributes betterC \
 		--inputdir  $< --outputdir $(BETTERCTESTS_DIR)
-	@$(DMD) $(DFLAGS) $(NODEFAULTLIB) -betterC $(UDFLAGS) -preview=dip1000 -run $(BETTERCTESTS_DIR)/$(subst /,_,$<)
+	@$(DMD) $(DFLAGS) $(NODEFAULTLIB) -betterC $(UDFLAGS) -run $(BETTERCTESTS_DIR)/$(subst /,_,$<)
 
 ################################################################################