diff --git a/2021/Makefile b/2021/Makefile
index def2d8e..da34a7c 100644
--- a/2021/Makefile
+++ b/2021/Makefile
@@ -11,12 +11,13 @@ black := $(PYTHON) -m black
 mypy := $(PYTHON) -m mypy
 ruff := $(PYTHON) -m ruff
 
-srcs := $(wildcard *.py)
-answers := $(subst puzzle,answer,$(srcs:.py=.txt))
+ext := .py
+srcs := $(wildcard puzzle_*$(ext))
+answers := $(subst puzzle,answer,$(srcs:$(ext)=.txt))
 
 include $(CURDIR)/../mk-common/common.mk
 
-answer_%.txt: puzzle_%.py input_%.txt
+answer_%.txt: puzzle_%$(ext) input_%.txt
 	$(PYTHON) ./$< < $(filter-out $<, $^) | tee $@
 
 .PHONY: lint
diff --git a/2022/Makefile b/2022/Makefile
index a707312..c5eec27 100644
--- a/2022/Makefile
+++ b/2022/Makefile
@@ -7,8 +7,9 @@ SHELL := bash
 
 NIM ?= nim
 
-srcs := $(wildcard puzzle_*.nim)
-answers := $(subst puzzle,answer,$(srcs:.nim=.txt))
+ext := .nim
+srcs := $(wildcard puzzle_*$(ext))
+answers := $(subst puzzle,answer,$(srcs:$(ext)=.txt))
 
 include $(CURDIR)/../mk-common/common.mk
 
@@ -16,7 +17,7 @@ answer_%.txt: puzzle_% input_%.txt
 	./$< < $(filter-out $<, $^) | tee $@
 
 .NOTINTERMEDIATE: puzzle_%
-puzzle_%: puzzle_%.nim nim.cfg
+puzzle_%: puzzle_%$(ext) nim.cfg
 	$(NIM) c $<
 
 .PHONY: format