diff --git a/src/Makefile b/src/Makefile
index 16c3e97..7996688 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -1,7 +1,7 @@
 
-CXX = g++
-CXXFLAGS = -O3
-AR = ar
+CXX ?= g++
+CXXFLAGS ?= -O3
+AR ?= ar
 
 all: libosmpbf.a ../include/osmpbf/fileformat.pb.h ../include/osmpbf/osmformat.pb.h
 
diff --git a/tools/Makefile b/tools/Makefile
index b9fc26b..db134fc 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -1,7 +1,7 @@
 
-CXX = g++
-CXXFLAGS = -g -I../include
-LDFLAGS = -L../src -lpthread -lz -lprotobuf-lite -losmpbf
+CXX ?= g++
+CXXFLAGS ?= -g -I../include
+LDFLAGS ?= -L../src -lpthread -lz -lprotobuf-lite -losmpbf
 
 all: osmpbf-outline