diff --git a/build.sh b/build.sh
index 9c62224..3b0ee9a 100755
--- a/build.sh
+++ b/build.sh
@@ -4,5 +4,7 @@ arduino-cli config --additional-urls https://raw.githubusercontent.com/espressif
 arduino-cli core update-index
 arduino-cli core install esp32:esp32
 arduino-cli upgrade
+# uBitcoin is broken on esp32 3.x.x
+arduino-cli core install esp32:esp32@2.0.17
 arduino-cli lib install uBitcoin WebSockets ArduinoJson base64 Button WiFiManager Nostr # QRCode ESP32Ping
 arduino-cli compile --build-path build --fqbn esp32:esp32:esp32 --build-property "build.partitions=min_spiffs" --build-property "upload.maximum_size=1966080" nostrZapLamp