diff --git a/Makefile b/Makefile
index 5656da5..f57c121 100644
--- a/Makefile
+++ b/Makefile
@@ -5,8 +5,8 @@ CPPFLAGS=-std=gnu++11 -I../include -I../../include
 LIBSFLAGS=
 WARNFLAGS=-Wall
 
-CFLAGS=$(OPTFLAGS) $(EXPORTFLAGS) $(WARNFLAGS) $(CPPFLAGS)
-LDFLAGS=$(OPTFLAGS) $(EXPORTFLAGS) $(WARNFLAGS) $(LIBSFLAGS)
+CFLAGS+=$(OPTFLAGS) $(EXPORTFLAGS) $(WARNFLAGS) $(CPPFLAGS)
+LDFLAGS+=$(OPTFLAGS) $(EXPORTFLAGS) $(WARNFLAGS) $(LIBSFLAGS)
 
 CC=g++
 
diff --git a/src/Makefile b/src/Makefile
index 24e994b..a33b399 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -5,8 +5,8 @@ CPPFLAGS=-std=gnu++11 -I../include
 LIBSFLAGS=-ldl -lpthread $(MODLIBS)
 WARNFLAGS=-Wall
 
-CFLAGS=$(OPTFLAGS) $(EXPORTFLAGS) $(WARNFLAGS) $(CPPFLAGS)
-LDFLAGS=$(OPTFLAGS) $(EXPORTFLAGS) $(WARNFLAGS) $(LIBSFLAGS)
+CFLAGS+=$(OPTFLAGS) $(EXPORTFLAGS) $(WARNFLAGS) $(CPPFLAGS)
+LDFLAGS+=$(OPTFLAGS) $(EXPORTFLAGS) $(WARNFLAGS) $(LIBSFLAGS)
 
 CC=g++