diff --git a/Makefile b/Makefile
index 1f8e1be58..5bddebc12 100644
--- a/Makefile
+++ b/Makefile
@@ -3,7 +3,11 @@ with_transcoding ?= yes
 
 ifeq ($(DO_ASAN_FLAGS),1)
 ASAN_FLAGS = -ggdb -O0 -fsanitize=address -fsanitize=leak -fsanitize=undefined
-CFLAGS ?= -Wall -Wextra -Wno-sign-compare -Wno-unused-parameter -Wstrict-prototypes
+ifeq ($(origin CFLAGS),undefined)
+CFLAGS := -Wall -Wextra -Wno-sign-compare -Wno-unused-parameter -Wstrict-prototypes
+else
+CFLAGS := $(CFLAGS)
+endif
 CFLAGS += $(ASAN_FLAGS)
 CFLAGS += -DASAN_BUILD
 LDFLAGS += $(ASAN_FLAGS)
diff --git a/daemon/Makefile b/daemon/Makefile
index 8599cdab5..51274b781 100644
--- a/daemon/Makefile
+++ b/daemon/Makefile
@@ -3,9 +3,12 @@ TARGET=		rtpengine
 with_iptables_option ?= yes
 with_transcoding ?= yes
 
-
-CFLAGS?=	-g -Wall -Wextra -Wno-sign-compare -Wno-unused-parameter -Wstrict-prototypes -Werror=return-type \
+ifeq ($(origin CFLAGS),undefined)
+CFLAGS:=	-g -Wall -Wextra -Wno-sign-compare -Wno-unused-parameter -Wstrict-prototypes -Werror=return-type \
 		-Wshadow
+else
+CFLAGS:=	$(CFLAGS)
+endif
 CFLAGS+=	-pthread
 CFLAGS+=	-std=c11
 CFLAGS+=	$(shell pkg-config --cflags glib-2.0)
@@ -49,7 +52,7 @@ endif
 #CFLAGS+=	-DSRTCP_KEY_DERIVATION_RFC_COMPLIANCE
 #CFLAGS+=	-DSTRICT_SDES_KEY_LIFETIME
 
-LDLIBS=		-lm -ldl
+LDLIBS:=	-lm -ldl
 LDLIBS+=	$(shell pkg-config --libs glib-2.0)
 LDLIBS+=	$(shell pkg-config --libs gthread-2.0)
 LDLIBS+=	$(shell pkg-config --libs zlib)
diff --git a/debian/rules b/debian/rules
index 861816ee8..4792edbe2 100755
--- a/debian/rules
+++ b/debian/rules
@@ -21,7 +21,7 @@ endif
 
 export FIXTURES_PATH = /usr/share/rtpengine-perftest
 
-export deb_systemdsystemunitdir = $(shell pkg-config --variable=systemdsystemunitdir systemd)
+export deb_systemdsystemunitdir := $(shell pkg-config --variable=systemdsystemunitdir systemd)
 
 %:
 	dh $@
diff --git a/kernel-module/Makefile b/kernel-module/Makefile
index a4bf76100..70d0a5599 100644
--- a/kernel-module/Makefile
+++ b/kernel-module/Makefile
@@ -4,12 +4,12 @@ KBUILD := $(KSRC)
 M      ?= $(PWD)
 
 ifeq ($(RTPENGINE_VERSION),)
-  DPKG_PRSCHNGLG= $(shell which dpkg-parsechangelog 2>/dev/null)
-  DEB_CHANGELOG=$(shell test -f $(M)/../debian/changelog && echo $(M)/../debian/changelog || echo $(M)/debian/changelog)
+  DPKG_PRSCHNGLG := $(shell which dpkg-parsechangelog 2>/dev/null)
+  DEB_CHANGELOG := $(shell test -f $(M)/../debian/changelog && echo $(M)/../debian/changelog || echo $(M)/debian/changelog)
   ifneq ($(DPKG_PRSCHNGLG),)
-    DPKG_PRSCHNGLG=$(shell dpkg-parsechangelog -l$(DEB_CHANGELOG) | awk '/^Version: / {print $$2}')
+    DPKG_PRSCHNGLG := $(shell dpkg-parsechangelog -l$(DEB_CHANGELOG) | awk '/^Version: / {print $$2}')
   endif
-  GIT_BR_COMMIT=git-$(shell cd $(M) && git rev-parse --abbrev-ref --symbolic-full-name HEAD 2> /dev/null)-$(shell cd $(M) && git rev-parse --short HEAD 2> /dev/null)
+  GIT_BR_COMMIT := git-$(shell cd $(M) && git rev-parse --abbrev-ref --symbolic-full-name HEAD 2> /dev/null)-$(shell cd $(M) && git rev-parse --short HEAD 2> /dev/null)
 
   ifneq ($(DPKG_PRSCHNGLG),)
     RTPENGINE_VERSION+=$(DPKG_PRSCHNGLG)
diff --git a/lib/g729.Makefile b/lib/g729.Makefile
index 20f4ea613..abeef264a 100644
--- a/lib/g729.Makefile
+++ b/lib/g729.Makefile
@@ -1,8 +1,8 @@
 ifeq (,$(filter pkg.ngcp-rtpengine.nobcg729,${DEB_BUILD_PROFILES}))
 # look for bcg729
 # system pkg-config
-ifeq ($(shell pkg-config --exists libbcg729 && echo yes),yes)
-have_bcg729 := yes
+have_bcg729 := $(shell pkg-config --exists libbcg729 && echo yes)
+ifeq ($(have_bcg729),yes)
 bcg729_inc := $(shell pkg-config --cflags libbcg729)
 bcg729_lib := $(shell pkg-config --libs libbcg729)
 else
diff --git a/lib/lib.Makefile b/lib/lib.Makefile
index 568d14a41..8bc92e4f6 100644
--- a/lib/lib.Makefile
+++ b/lib/lib.Makefile
@@ -5,22 +5,22 @@ ifeq ($(RTPENGINE_ROOT_DIR),)
 	RTPENGINE_ROOT_DIR=..
 endif
 
-HAVE_DPKG_PARSECHANGELOG?=$(shell which dpkg-parsechangelog 2>/dev/null)
+HAVE_DPKG_PARSECHANGELOG := $(shell which dpkg-parsechangelog 2>/dev/null)
 
 ifeq ($(RELEASE_DATE),)
   ifneq ($(HAVE_DPKG_PARSECHANGELOG),)
-    RELEASE_DATE=$(shell date -u -d "@$$(dpkg-parsechangelog -l$(RTPENGINE_ROOT_DIR)/debian/changelog -STimestamp)" '+%F')
+    RELEASE_DATE := $(shell date -u -d "@$$(dpkg-parsechangelog -l$(RTPENGINE_ROOT_DIR)/debian/changelog -STimestamp)" '+%F')
   endif
   ifeq ($(RELEASE_DATE),)
-    RELEASE_DATE=undefined
+    RELEASE_DATE := undefined
   endif
 endif
 
 ifeq ($(RTPENGINE_VERSION),)
   ifneq ($(HAVE_DPKG_PARSECHANGELOG),)
-    DPKG_PRSCHNGLG=$(shell dpkg-parsechangelog -l$(RTPENGINE_ROOT_DIR)/debian/changelog | awk '/^Version: / {print $$2}')
+    DPKG_PRSCHNGLG := $(shell dpkg-parsechangelog -l$(RTPENGINE_ROOT_DIR)/debian/changelog | awk '/^Version: / {print $$2}')
   endif
-  GIT_BR_COMMIT=git-$(shell git rev-parse --abbrev-ref --symbolic-full-name HEAD 2> /dev/null)-$(shell git rev-parse --short HEAD 2> /dev/null)
+  GIT_BR_COMMIT := git-$(shell git rev-parse --abbrev-ref --symbolic-full-name HEAD 2> /dev/null)-$(shell git rev-parse --short HEAD 2> /dev/null)
 
   ifneq ($(DPKG_PRSCHNGLG),)
     RTPENGINE_VERSION+=$(DPKG_PRSCHNGLG)
@@ -36,9 +36,7 @@ endif
 CFLAGS+=	-DRTPENGINE_VERSION="\"$(RTPENGINE_VERSION)\""
 
 # look for libsystemd
-ifeq ($(shell pkg-config --exists libsystemd && echo yes),yes)
-have_libsystemd := yes
-endif
+have_libsystemd := $(shell pkg-config --exists libsystemd && echo yes)
 ifeq ($(have_libsystemd),yes)
 CFLAGS+=	$(shell pkg-config --cflags libsystemd)
 CFLAGS+=	-DHAVE_LIBSYSTEMD
@@ -47,9 +45,7 @@ endif
 
 # look for liburing
 ifeq (,$(filter pkg.ngcp-rtpengine.nouring,${DEB_BUILD_PROFILES}))
-ifeq ($(shell pkg-config --atleast-version=2.3 liburing && echo yes),yes)
-have_liburing := yes
-endif
+have_liburing := $(shell pkg-config --atleast-version=2.3 liburing && echo yes)
 ifeq ($(have_liburing),yes)
 CFLAGS+=	$(shell pkg-config --cflags liburing)
 CFLAGS+=	-DHAVE_LIBURING
@@ -66,7 +62,7 @@ LDFLAGS += -rdynamic
 
 ifneq ($(DBG),yes)
   ifeq (,$(filter $(CFLAGS),-O0))
-    DPKG_BLDFLGS=	$(shell which dpkg-buildflags 2>/dev/null)
+    DPKG_BLDFLGS := $(shell which dpkg-buildflags 2>/dev/null)
     ifneq ($(DPKG_BLDFLGS),)
       # support http://wiki.debian.org/Hardening for >=wheezy
       CFLAGS+=	$(shell dpkg-buildflags --get CFLAGS)
diff --git a/lib/mqtt.Makefile b/lib/mqtt.Makefile
index 552007de1..37d687442 100644
--- a/lib/mqtt.Makefile
+++ b/lib/mqtt.Makefile
@@ -1,10 +1,7 @@
-ifeq ($(shell pkg-config --exists libmosquitto && echo yes),yes)
-have_mqtt := yes
+have_mqtt := $(shell pkg-config --exists libmosquitto && echo yes)
+ifeq ($(have_mqtt),yes)
 mqtt_inc := $(shell pkg-config --cflags libmosquitto)
 mqtt_lib := $(shell pkg-config --libs libmosquitto)
-endif
-
-ifeq ($(have_mqtt),yes)
 CFLAGS+=	-DHAVE_MQTT
 CFLAGS+=	$(mqtt_inc)
 endif
diff --git a/perf-tester/Makefile b/perf-tester/Makefile
index 387edbd12..fa7a50c7c 100644
--- a/perf-tester/Makefile
+++ b/perf-tester/Makefile
@@ -2,8 +2,12 @@ TARGET = rtpengine-perftest
 
 FIXTURES_PATH ?= ../fixtures
 
+ifeq ($(origin CFLAGS),undefined)
 CFLAGS ?= -g -Wall -Wextra -Wno-sign-compare -Wno-unused-parameter -Wstrict-prototypes -Werror=return-type \
 		-Wshadow
+else
+CFLAGS := $(CFLAGS)
+endif
 
 CFLAGS += -pthread
 CFLAGS += -std=c11
@@ -25,7 +29,7 @@ CFLAGS += $(shell pkg-config --cflags ncursesw)
 CFLAGS += -DWITH_TRANSCODING
 CFLAGS += $(shell pkg-config --cflags openssl)
 
-LDLIBS = -lm -ldl
+LDLIBS := -lm -ldl
 LDLIBS += $(shell pkg-config --libs glib-2.0)
 LDLIBS += $(shell pkg-config --libs json-glib-1.0)
 LDLIBS += $(shell pkg-config --libs gthread-2.0)
diff --git a/recording-daemon/Makefile b/recording-daemon/Makefile
index 22fa86c52..8fe8f75e4 100644
--- a/recording-daemon/Makefile
+++ b/recording-daemon/Makefile
@@ -1,7 +1,11 @@
 TARGET=		rtpengine-recording
 
+ifeq ($(origin CFLAGS),undefined)
 CFLAGS?=	-g -Wall -Wextra -Wno-sign-compare -Wno-unused-parameter -Wstrict-prototypes -Werror=return-type \
 		-Wshadow
+else
+CFLAGS:=	$(CFLAGS)
+endif
 CFLAGS+=	-pthread -I. -I../lib/ -I../kernel-module/
 CFLAGS+=	-std=c11
 CFLAGS+=	-D_GNU_SOURCE -D_POSIX_SOURCE -D_POSIX_C_SOURCE
@@ -19,7 +23,7 @@ CFLAGS+=	$(shell mysql_config --cflags)
 CFLAGS+=	$(shell pkg-config --cflags openssl)
 CFLAGS+=	$(shell pkg-config --cflags libcurl)
 
-LDLIBS=		-lm -ldl
+LDLIBS:=	-lm -ldl
 LDLIBS+=	$(shell pkg-config --libs glib-2.0)
 LDLIBS+=	$(shell pkg-config --libs json-glib-1.0)
 LDLIBS+=	$(shell pkg-config --libs gthread-2.0)
diff --git a/t/Makefile b/t/Makefile
index 862c08548..cc0315ea0 100644
--- a/t/Makefile
+++ b/t/Makefile
@@ -2,8 +2,12 @@ TARGET=		all-tests
 
 with_transcoding ?= yes
 
+ifeq ($(origin CFLAGS),undefined)
 CFLAGS?=	-g -Wall -Wextra -Wno-sign-compare -Wno-unused-parameter -Wstrict-prototypes -Werror=return-type \
 		-Wshadow
+else
+CFLAGS:=	$(CFLAGS)
+endif
 PRELOAD_CFLAGS := $(CFLAGS)
 CFLAGS+=	-pthread
 CFLAGS+=	-std=c11
@@ -38,7 +42,7 @@ else
 CFLAGS+=	-DWITHOUT_CODECLIB
 endif
 
-LDLIBS=		-lm -ldl
+LDLIBS:=	-lm -ldl
 LDLIBS+=	$(shell pkg-config --libs glib-2.0)
 LDLIBS+=	$(shell pkg-config --libs gthread-2.0)
 LDLIBS+=	$(shell pkg-config --libs libcrypto)