diff --git a/Makefile b/Makefile
index 8bf2699c5..d2508c5a0 100644
--- a/Makefile
+++ b/Makefile
@@ -39,8 +39,8 @@ all: top-all
 YOSYS_SRC := $(dir $(firstword $(MAKEFILE_LIST)))
 VPATH := $(YOSYS_SRC)
 
-CXXFLAGS = -Wall -Wextra -ggdb -I. -I"$(YOSYS_SRC)" -MD -D_YOSYS_ -fPIC -I$(DESTDIR)/include
-LDFLAGS = -L$(DESTDIR)/lib
+CXXFLAGS += -Wall -Wextra -ggdb -I. -I"$(YOSYS_SRC)" -MD -D_YOSYS_ -fPIC -I$(DESTDIR)/include
+LDFLAGS += -L$(DESTDIR)/lib
 LDLIBS = -lstdc++ -lm
 SED = sed
 BISON = bison
@@ -307,11 +307,11 @@ libyosys.so: $(filter-out kernel/driver.o,$(OBJS))
 
 %.o: %.cc
 	$(Q) mkdir -p $(dir $@)
-	$(P) $(CXX) -o $@ -c $(CXXFLAGS) $<
+	$(P) $(CXX) -o $@ -c $(CPPFLAGS) $(CXXFLAGS) $<
 
 %.o: %.cpp
 	$(Q) mkdir -p $(dir $@)
-	$(P) $(CXX) -o $@ -c $(CXXFLAGS) $<
+	$(P) $(CXX) -o $@ -c $(CPPFLAGS) $(CXXFLAGS) $<
 
 kernel/version_$(GIT_REV).cc: $(YOSYS_SRC)/Makefile
 	$(P) rm -f kernel/version_*.o kernel/version_*.d kernel/version_*.cc
@@ -319,9 +319,9 @@ kernel/version_$(GIT_REV).cc: $(YOSYS_SRC)/Makefile
 			$(CXX) --version | tr ' ()' '\n' | grep '^[0-9]' | head -n1` $(filter -f% -m% -O% -DNDEBUG,$(CXXFLAGS)))\"; }" > kernel/version_$(GIT_REV).cc
 
 yosys-config: misc/yosys-config.in
-	$(P) $(SED) -e 's,@CXXFLAGS@,$(subst -I. -I"$(YOSYS_SRC)",-I"$(TARGET_DATDIR)/include",$(CXXFLAGS)),;' \
-			-e 's,@CXX@,$(CXX),;' -e 's,@LDFLAGS@,$(LDFLAGS),;' -e 's,@LDLIBS@,$(LDLIBS),;' \
-			-e 's,@BINDIR@,$(TARGET_BINDIR),;' -e 's,@DATDIR@,$(TARGET_DATDIR),;' < $< > yosys-config
+	$(P) $(SED) -e 's#@CXXFLAGS@#$(subst -I. -I"$(YOSYS_SRC)",-I"$(TARGET_DATDIR)/include",$(CXXFLAGS))#;' \
+			-e 's#@CXX@#$(CXX)#;' -e 's#@LDFLAGS@#$(LDFLAGS)#;' -e 's#@LDLIBS@#$(LDLIBS)#;' \
+			-e 's#@BINDIR@#$(TARGET_BINDIR)#;' -e 's#@DATDIR@#$(TARGET_DATDIR)#;' < $< > yosys-config
 	$(Q) chmod +x yosys-config
 
 abc/abc-$(ABCREV)$(EXE):