diff --git a/Makefile b/Makefile
index 420fc3276..1c7f84ec6 100644
--- a/Makefile
+++ b/Makefile
@@ -13,7 +13,7 @@ YAML_TEST_TARGETS = $(patsubst $(GENERATOR_DIR)/%, $(YAML_TEST_DIR)/%, $(GENERAT
 GENERATOR_VENVS = $(patsubst $(GENERATOR_DIR)/%, $(GENERATOR_DIR)/%venv, $(GENERATORS))
 
 PY_SPEC_PHASE_0_TARGETS = $(PY_SPEC_DIR)/eth2spec/phase0/spec.py
-PY_SPEC_PHASE_1_TARGETS = $(PY_SPEC_DIR)/eth2spec/phase1/custody-game.py $(PY_SPEC_DIR)/eth2spec/phase1/shard-data-chains.py
+PY_SPEC_PHASE_1_TARGETS = $(PY_SPEC_DIR)/eth2spec/phase1/custody_game.py $(PY_SPEC_DIR)/eth2spec/phase1/shard_data_chains.py
 PY_SPEC_ALL_TARGETS = $(PY_SPEC_PHASE_0_TARGETS)
 
 
@@ -53,10 +53,10 @@ phase1: $(PY_SPEC_PHASE_1_TARGETS)
 $(PY_SPEC_DIR)/eth2spec/phase0/spec.py:
 	python3 $(SCRIPT_DIR)/phase0/build_spec.py  $(SPEC_DIR)/core/0_beacon-chain.md $@
 
-$(PY_SPEC_DIR)/eth2spec/phase1/custody-game.py:
+$(PY_SPEC_DIR)/eth2spec/phase1/custody_game.py:
 	python3 $(SCRIPT_DIR)/phase0/build_spec.py -p1  $(SPEC_DIR)/core/1_custody-game.md $@
 
-$(PY_SPEC_DIR)/eth2spec/phase1/shard-data-chains.py:
+$(PY_SPEC_DIR)/eth2spec/phase1/shard_data_chains.py:
 	python3 $(SCRIPT_DIR)/phase0/build_spec.py -p1 $(SPEC_DIR)/core/1_shard-data-chains.md $@