diff --git a/Makefile b/Makefile
index e4335f0..719d21b 100644
--- a/Makefile
+++ b/Makefile
@@ -2,7 +2,8 @@ VENV = poetry run
 ESP_TOOL = $(VENV) esptool.py --port $(ESP_PORT)
 MPYCROSS = $(VENV) mpy-cross
 AMPY = $(VENV) ampy --port $(ESP_PORT)
-JUPYTER_PYTHON_FILES = $(shell find src/*.ipynb | sed "s/ipynb/py/g")
+JUPYTER_FILES = $(shell find src/*.ipynb)
+JUPYTER_PYTHON_FILES = $(JUPYTER_FILES:ipynb=py)
 
 # Downloaded from https://micropython.org/download/ESP8266_GENERIC/
 MICRO_PYTHON_FIRMWARE = ESP8266_GENERIC-20240222-v1.22.2.bin