diff --git a/src/Makefile b/src/Makefile
index fb0c3ffe..2bdb3ee9 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -4,7 +4,13 @@
 # Copyright (C) 1996-2015 Markus Franz Xaver Johannes Oberhumer
 #
 
+# In GNU Make 4.0 this "MAKEFLAGS += -rR" is not executed immediately.
+# Instead, it is executed later, and we cannot rely on sequentiality
+# with respect to builtin variables.  So if we want to have no
+# dependencies on the default values of builtin variables,
+# then we cannot use builtin variables at all.
 MAKEFLAGS += -rR
+
 .SUFFIXES:
 export SHELL = /bin/sh
 override e = $($1) $(EXTRA_$1) $(upx_$1) $($(basename $(notdir $@)).$1)
@@ -26,30 +32,30 @@ ifneq ($(srcdir),.)
 VPATH := . $(srcdir)
 endif
 
-ifeq ($(CXX),)
-CXX = g++
+ifeq ($(upx_CXX),)
+upx_CXX = g++
 endif
-ifneq ($(findstring $(firstword $(CXX)),g++),)
+ifneq ($(findstring $(firstword $(upx_CXX)),g++),)
 USE_GNUC ?= 1
 endif
 ifeq ($(USE_GNUC),1)
 ifeq ($(DEBUG),1)
-CXXFLAGS += -O0 -g
+upx_CXXFLAGS += -O0 -g
 else
-CXXFLAGS += -O2
+upx_CXXFLAGS += -O2
 LDFLAGS += -s
 endif
 # some gcc versions suffer over-agressive aliasing and wrapv optimization features/bugs
-CXXFLAGS_OPTIMIZE_STRICT_ALIASING ?= -fno-strict-aliasing
-CXXFLAGS_OPTIMIZE_WRAPV ?= -fwrapv
-CXXFLAGS += $(CXXFLAGS_OPTIMIZE_STRICT_ALIASING)
-CXXFLAGS += $(CXXFLAGS_OPTIMIZE_WRAPV)
-CXXFLAGS += -Wall -W -Wcast-align -Wcast-qual -Wpointer-arith -Wshadow -Wwrite-strings
-CXXFLAGS_WERROR ?= -Werror
-CXXFLAGS += $(CXXFLAGS_WERROR)
+upx_CXXFLAGS_OPTIMIZE_STRICT_ALIASING ?= -fno-strict-aliasing
+upx_CXXFLAGS_OPTIMIZE_WRAPV ?= -fwrapv
+upx_CXXFLAGS += $(upx_CXXFLAGS_OPTIMIZE_STRICT_ALIASING)
+upx_CXXFLAGS += $(upx_CXXFLAGS_OPTIMIZE_WRAPV)
+upx_CXXFLAGS += -Wall -W -Wcast-align -Wcast-qual -Wpointer-arith -Wshadow -Wwrite-strings
+upx_CXXFLAGS_WERROR ?= -Werror
+upx_CXXFLAGS += $(upx_CXXFLAGS_WERROR)
 endif
-CPPFLAGS += $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES)
-CXXLD ?= $(CXX)
+upx_CPPFLAGS += $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES)
+upx_CXXLD ?= $(upx_CXX)
 
 exeext ?= .out
 libext ?= .a
@@ -66,6 +72,7 @@ endif
 LIBS += -lucl -lz
 # you should set envvar UPX_LZMADIR to point to your unpacked LZMA SDK
 include $(top_srcdir)/src/stub/src/c/Makevars.lzma
+$(info UPX_LZMA_VERSION=$(UPX_LZMA_VERSION))
 ifneq ($(UPX_LZMA_VERSION),)
 DEFS += -DWITH_LZMA=$(UPX_LZMA_VERSION)
 INCLUDES += -I$(UPX_LZMADIR)
@@ -77,32 +84,32 @@ all: upx$(exeext) | .depend
 
 upx$(exeext): $(upx_OBJECTS) $(upx_DEPENDENCIES)
 	$($(notdir $@).PRE_LINK_STEP)
-	$(strip $(CXXLD) $(call e,CPPFLAGS) $(call e,CXXFLAGS) $(call e,LDFLAGS) -o $@ $(upx_OBJECTS) $(call e,LDADD) $(call e,LIBS))
+	$(strip $(upx_CXXLD) $(call e,upx_CPPFLAGS) $(call e,upx_CXXFLAGS) $(call e,LDFLAGS) -o $@ $(upx_OBJECTS) $(call e,LDADD) $(call e,LIBS))
 	$($(notdir $@).POST_LINK_STEP)
 
 %.o : %.cpp | .depend
-	$(strip $(CXX) $(call e,CPPFLAGS) $(call e,CXXFLAGS) -o $@ -c $<)
+	$(strip $(upx_CXX) $(call e,upx_CPPFLAGS) $(call e,upx_CXXFLAGS) -o $@ -c $<)
 
 .depend: $(sort $(wildcard $(srcdir)/*.cpp $(srcdir)/*.h)) $(MAKEFILE_LIST)
 	@rm -f $@
 ifeq ($(USE_GNUC),1)
 	@echo "Updating $@"
-	@$(strip $(CXX) $(call e,CPPFLAGS) -MM) $(filter %.cpp,$^) > $@
+	@$(strip $(upx_CXX) $(call e,upx_CPPFLAGS) -MM) $(filter %.cpp,$^) > $@
 else
 	touch $@
 endif
 
 
 ifeq ($(USE_GNUC),1)
-##compress_lzma$(objext) : CXXFLAGS += -O3 -fomit-frame-pointer
-compress_lzma$(objext) : CXXFLAGS += -Wno-cast-qual
-compress_lzma$(objext) : CXXFLAGS += -Wno-shadow
+##compress_lzma$(objext) : upx_CXXFLAGS += -O3 -fomit-frame-pointer
+compress_lzma$(objext) : upx_CXXFLAGS += -Wno-cast-qual
+compress_lzma$(objext) : upx_CXXFLAGS += -Wno-shadow
 ifeq ($(UPX_LZMA_VERSION),0x443)
-compress_lzma$(objext) : CXXFLAGS += -Wno-non-virtual-dtor
-compress_lzma$(objext) : CXXFLAGS += -Wno-unused
+compress_lzma$(objext) : upx_CXXFLAGS += -Wno-non-virtual-dtor
+compress_lzma$(objext) : upx_CXXFLAGS += -Wno-unused
 endif
 # needed for gcc-4.3:
-compress_lzma$(objext) : CXXFLAGS += -Wno-error
+compress_lzma$(objext) : upx_CXXFLAGS += -Wno-error
 endif