diff --git a/Makefile b/Makefile
index 99c8660..b973201 100644
--- a/Makefile
+++ b/Makefile
@@ -82,7 +82,17 @@ endef
 .PHONY: default
 default:
 
-include makefile.mk
+
+INCLUDE += include
+
+SRC_DIR = src
+include $(SRC_DIR)/makefile.mk
+
+TOOLS_DIR = tools
+-include $(TOOLS_DIR)/makefile.mk
+
+TEST_DIR := test
+-include $(TEST_DIR)/makefile.mk
 
 
 #
diff --git a/makefile.mk b/src/makefile.mk
similarity index 91%
rename from makefile.mk
rename to src/makefile.mk
index a7b3976..968ec43 100644
--- a/makefile.mk
+++ b/src/makefile.mk
@@ -14,9 +14,6 @@
 # limitations under the License.
 #
 
-INCLUDE += include
-SRC_DIR := src
-
 liblc3_src += \
     $(SRC_DIR)/attdet.c \
     $(SRC_DIR)/bits.c \
@@ -36,6 +33,3 @@ liblc3_cflags += -ffast-math
 $(eval $(call add-lib,liblc3))
 
 default: liblc3
-
--include tools/makefile.mk
--include test/makefile.mk
diff --git a/test/makefile.mk b/test/makefile.mk
index b52b7ac..a7bcb04 100644
--- a/test/makefile.mk
+++ b/test/makefile.mk
@@ -14,8 +14,6 @@
 # limitations under the License.
 #
 
-TEST_DIR := test
-
 test_py:
 	$(V)cd $(TEST_DIR) && python3 setup.py && PYTHONPATH=build python3 run.py
 
diff --git a/tools/makefile.mk b/tools/makefile.mk
index 066003e..cc19c29 100644
--- a/tools/makefile.mk
+++ b/tools/makefile.mk
@@ -14,9 +14,6 @@
 # limitations under the License.
 #
 
-TOOLS_DIR = tools
-
-
 elc3_src += \
     $(TOOLS_DIR)/elc3.c \
     $(TOOLS_DIR)/lc3bin.c \