--- a/Makefile
+++ b/Makefile
@@ -81,8 +81,6 @@
   ifeq ($(findstring $(OSTYPE), amiga haiku mac),)
     CFLAGS += -minline-all-stringops
   endif
-else
-  CFLAGS += -O
 endif
 
 ifdef DEBUG
@@ -101,6 +99,7 @@
   endif
 else
   CFLAGS += -DNDEBUG
+  CXXFLAGS += -DNDEBUG
 endif
 
 ifneq ($(PROFILE),)
@@ -114,6 +113,7 @@
 ifneq ($(MULTI_THREAD),)
   ifeq ($(shell expr $(MULTI_THREAD) \>= 1), 1)
     CFLAGS += -DMULTI_THREAD
+    CXXFLAGS += -DMULTI_THREAD
     ifeq ($(OSTYPE),mingw)
 #use lpthreadGC2d for debug alternatively
       LDFLAGS += -lpthreadGC2
@@ -132,11 +132,13 @@
     endif
     ifneq ($(REV),)
       CFLAGS  += -DREVISION="$(REV)"
+      CXXFLAGS  += -DREVISION="$(REV)"
     endif
   endif
 endif
 
 CFLAGS   += -Wall -W -Wcast-qual -Wpointer-arith -Wcast-align $(FLAGS)
+CXXFLAGS += -Wall -W -Wcast-qual -Wpointer-arith -Wcast-align $(FLAGS)
 CCFLAGS  += -Wstrict-prototypes
 
 
@@ -492,6 +494,7 @@
     SDL_LDFLAGS := $(shell $(SDL_CONFIG) --libs)
   endif
   CFLAGS += $(SDL_CFLAGS)
+  CXXFLAGS += $(SDL_CFLAGS)
   LIBS   += $(SDL_LDFLAGS)
 endif
 
@@ -523,6 +526,7 @@
     SDL_LDFLAGS := $(shell $(SDL2_CONFIG) --libs)
   endif
   CFLAGS += $(SDL_CFLAGS)
+  CXXFLAGS += $(SDL_CFLAGS)
   LIBS   += $(SDL_LDFLAGS)
 endif
 
@@ -538,6 +542,7 @@
     SDL_LDFLAGS := $(shell $(SDL_CONFIG) --libs)
   endif
   CFLAGS += $(SDL_CFLAGS)
+  CXXFLAGS += $(SDL_CFLAGS)
   LIBS   += $(SDL_LDFLAGS) -lSDL_mixer
 endif
 
@@ -564,6 +569,7 @@
     SDL_LDFLAGS := $(shell $(SDL_CONFIG) --libs)
   endif
   CFLAGS += $(SDL_CFLAGS)
+  CXXFLAGS += $(SDL_CFLAGS)
   LIBS   += $(SDL_LDFLAGS) -lglew32
   ifeq ($(OSTYPE),mingw)
     LIBS += -lopengl32
@@ -579,6 +585,7 @@
 endif
 
 CFLAGS += -DCOLOUR_DEPTH=$(COLOUR_DEPTH)
+CXXFLAGS += -DCOLOUR_DEPTH=$(COLOUR_DEPTH)
 
 ifneq ($(findstring $(OSTYPE), cygwin mingw),)
   SOURCES += simres.rc
@@ -586,7 +593,6 @@
 endif
 
 CCFLAGS  += $(CFLAGS)
-CXXFLAGS += $(CFLAGS)
 
 BUILDDIR ?= build/$(CFG)
 PROGDIR  ?= $(BUILDDIR)