diff --git a/ip2net/Makefile b/ip2net/Makefile
index 97a53d7..2d2756e 100644
--- a/ip2net/Makefile
+++ b/ip2net/Makefile
@@ -1,5 +1,6 @@
 CC ?= gcc
-CFLAGS += -std=gnu99 -O3
+CFLAGS ?= -O3
+CFLAGS += -std=gnu99
 CFLAGS_BSD = -Wno-address-of-packed-member
 CFLAGS_WIN = -static
 LIBS = 
diff --git a/mdig/Makefile b/mdig/Makefile
index 58bc4b4..11c2e6d 100644
--- a/mdig/Makefile
+++ b/mdig/Makefile
@@ -1,5 +1,6 @@
 CC ?= gcc
-CFLAGS += -std=gnu99 -O3
+CFLAGS ?= -O3
+CFLAGS += -std=gnu99
 CFLAGS_BSD = -Wno-address-of-packed-member
 CFLAGS_WIN = -static
 LIBS = -lpthread
diff --git a/nfq/Makefile b/nfq/Makefile
index 783f437..1ca8568 100644
--- a/nfq/Makefile
+++ b/nfq/Makefile
@@ -1,5 +1,6 @@
 CC ?= gcc
-CFLAGS += -std=gnu99 -O3
+CFLAGS ?= -O3
+CFLAGS += -std=gnu99
 CFLAGS_BSD = -Wno-address-of-packed-member
 CFLAGS_MAC = -mmacosx-version-min=10.8
 CFLAGS_CYGWIN = -Wno-address-of-packed-member -static
diff --git a/tpws/Makefile b/tpws/Makefile
index 52b72f7..af2a2ec 100644
--- a/tpws/Makefile
+++ b/tpws/Makefile
@@ -1,5 +1,6 @@
 CC ?= gcc
-CFLAGS += -std=gnu99 -O3
+CFLAGS ?= -O3
+CFLAGS += -std=gnu99
 CFLAGS_BSD = -Wno-address-of-packed-member
 LIBS = -lz -lpthread
 SRC_FILES = *.c