--- a/bandwidth2/Makefile
+++ b/bandwidth2/Makefile
@@ -1,6 +1,6 @@
 P=bandwidth2
 OBJECTS=
-CFLAGS=-g -Wall -Werror -O2 -std=c11
+CFLAGS ?= -g -Wall -Werror -O2 -std=c11
 LDLIBS=
 
 $(P): $(OBJECTS)
--- a/brightness/Makefile
+++ b/brightness/Makefile
@@ -1,6 +1,6 @@
-CC=gcc
-AS=as
-LD=ld
+CC ?= gcc
+AS ?= as
+LD ?= ld
 OBJDUMP=objdump
 OBJCOPY=objcopy
 SIZE=size
@@ -16,14 +16,14 @@
 
 PRG = brightness
 INCLUDES := -Iinc
-CFLAGS := $(INCLUDES) $(DEFS) $(WARN_LEVEL) -pipe -O0 -g3 -std=c11
+CFLAGS ?= -pipe -O0 -g3 -std=c11
 
 debug: CFLAGS += -O0 -g3
 debug: all
 
 release: CFLAGS += -O2
 release: all
-LDFLAGS = $(LIBS) -ffunction-sections -Wl,--gc-sections
+LDFLAGS ?= -ffunction-sections -Wl,--gc-sections
 
 SRC_C := $(wildcard *.c) $(wildcard src/*.c)
 SRC_A := $(wildcard src/*.s)
@@ -41,7 +41,7 @@
 
 $(OBJ_DIR)/%.o: %.c
 	@mkdir -p $(@D)
-	$(CC) $(CFLAGS) -o $@ -c $<
+	$(CC) $(CFLAGS) $(INCLUDES) $(DEFS) $(WARN_LEVEL) -o $@ -c $<
 
 $(BIN_DIR)/$(PRG): $(OBJECTS)
 	@mkdir -p $(@D)
--- a/cpu_usage2/Makefile
+++ b/cpu_usage2/Makefile
@@ -1,6 +1,6 @@
 P=cpu_usage2
 OBJECTS=
-CFLAGS=-g -Wall -Werror -O2 -std=gnu11
+CFLAGS ?= -g -Wall -Werror -O2 -std=gnu11
 LDLIBS=
 
 $(P): $(OBJECTS)
--- a/memory2/Makefile
+++ b/memory2/Makefile
@@ -1,6 +1,6 @@
 P=memory2
 OBJECTS=
-CFLAGS=-g -Wall -Werror -O2 -std=c11
+CFLAGS ?= -g -Wall -Werror -O2 -std=c11
 LDLIBS=
 
 $(P): $(OBJECTS)