diff --git a/boards/msba2-common/tools/Makefile b/boards/msba2-common/tools/Makefile
index 8dbdcc242a..05db7a8f5f 100644
--- a/boards/msba2-common/tools/Makefile
+++ b/boards/msba2-common/tools/Makefile
@@ -1,4 +1,4 @@
-CFLAGS = -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"$(@:%.o=%.d)" -MT"$(@:%.o=%.d)"
+CFLAGS += -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"$(@:%.o=%.d)" -MT"$(@:%.o=%.d)"
 CC = gcc
 prefix=/usr/local
 
diff --git a/boards/redbee-econotag/Makefile.include b/boards/redbee-econotag/Makefile.include
index 19179c3c2d..addee0b20e 100644
--- a/boards/redbee-econotag/Makefile.include
+++ b/boards/redbee-econotag/Makefile.include
@@ -5,7 +5,7 @@ export CPU = mc1322x
 export PREFIX = @arm-none-eabi-
 export CC = @$(PREFIX)gcc
 export AR = @$(PREFIX)ar
-export CFLAGS = -std=gnu99 -march=armv4t -mtune=arm7tdmi-s -mlong-calls \
+export CFLAGS += -std=gnu99 -march=armv4t -mtune=arm7tdmi-s -mlong-calls \
 		-msoft-float -mthumb-interwork -fno-strict-aliasing -fno-common \
 		-ffixed-r8 -ffunction-sections -ffreestanding -fno-builtin \
 		-nodefaultlibs -Wcast-align -Wall -Wstrict-prototypes -Wextra \
diff --git a/cpu/arm_common/Makefile b/cpu/arm_common/Makefile
index 765464e60b..c9bf68070c 100644
--- a/cpu/arm_common/Makefile
+++ b/cpu/arm_common/Makefile
@@ -1,6 +1,6 @@
 MODULE =arm_common
 INCLUDES = -Iinclude -I../$(CPU)/include -I../../sys/lib -I../../drivers/include -I../../core/include -I../../sys/include -I../../hal/include -I../../.. -I../../sys/lib/fat
 
-CFLAGS = $(CFLAGS_BASIC)
+CFLAGS += $(CFLAGS_BASIC)
 include $(RIOTBASE)/Makefile.base