diff --git a/rbutil/mkimxboot/Makefile b/rbutil/mkimxboot/Makefile
index 2293d3939a..942ceb9ca7 100644
--- a/rbutil/mkimxboot/Makefile
+++ b/rbutil/mkimxboot/Makefile
@@ -7,7 +7,7 @@
 
 # We use the SB code available in the Rockbox utils/sbtools directory
 IMXTOOLS_DIR=../../utils/imxtools/
-CFLAGS = -I$(IMXTOOLS_DIR) -Wall
+CFLAGS += -I$(IMXTOOLS_DIR) -Wall
 CFLAGS += -std=c99
 
 OUTPUT = mkimxboot
diff --git a/rbutil/mkmpioboot/Makefile b/rbutil/mkmpioboot/Makefile
index 8b560d6b29..0a42e39217 100644
--- a/rbutil/mkmpioboot/Makefile
+++ b/rbutil/mkmpioboot/Makefile
@@ -7,7 +7,7 @@
 
 TARGET_DIR ?= $(shell pwd)/
 # We use the UCL code available in the Rockbox tools/ directory
-CFLAGS = -I../../tools/ucl/include -Wall
+CFLAGS += -I../../tools/ucl/include -Wall
 
 OUTPUT = mkmpioboot
 
diff --git a/rbutil/mktccboot/Makefile b/rbutil/mktccboot/Makefile
index 3bca0ba05e..31ad68e643 100644
--- a/rbutil/mktccboot/Makefile
+++ b/rbutil/mktccboot/Makefile
@@ -9,7 +9,7 @@
 
 # We use the Telechips code available in the Rockbox tools/ directory
 TOOLSDIR = ../../tools/
-CFLAGS := -O -g -W -Wall -Wshadow -pedantic -I$(TOOLSDIR)
+CFLAGS += -O -g -W -Wall -Wshadow -pedantic -I$(TOOLSDIR)
 
 OUTPUT = mktccboot
 
diff --git a/rbutil/tools/Makefile b/rbutil/tools/Makefile
index c598d928c6..d10e2528bf 100644
--- a/rbutil/tools/Makefile
+++ b/rbutil/tools/Makefile
@@ -3,7 +3,7 @@ ifndef V
 SILENT = @
 endif
 
-CFLAGS=-Wall -W -D_LARGEFILE64_SOURCE
+CFLAGS += -Wall -W -D_LARGEFILE64_SOURCE
 
 ifeq ($(findstring CYGWIN,$(shell uname)),CYGWIN)
 CROSS=
diff --git a/tools/rbspeex/Makefile b/tools/rbspeex/Makefile
index 86f00a1847..9f3f348a69 100644
--- a/tools/rbspeex/Makefile
+++ b/tools/rbspeex/Makefile
@@ -16,7 +16,7 @@ SPEEXSRC = ../../apps/codecs/libspeex
 INCLUDES = -I $(SPEEXSRC)
 SPEEXOPTS = -DHAVE_CONFIG_H -DROCKBOX_VOICE_ENCODER
 
-CFLAGS = $(SPEEXOPTS) $(INCLUDES) -O3 -fomit-frame-pointer -Wno-unused-parameter
+CFLAGS += $(SPEEXOPTS) $(INCLUDES) -O3 -fomit-frame-pointer -Wno-unused-parameter
 
 #build standalone win32 executables on cygwin
 ifeq ($(findstring CYGWIN,$(shell uname)),CYGWIN)