diff --git a/src/motion/MagnetometerThread.h b/src/motion/MagnetometerThread.h
index 1f558eb57..cf632867d 100644
--- a/src/motion/MagnetometerThread.h
+++ b/src/motion/MagnetometerThread.h
@@ -67,9 +67,11 @@ class MagnetometerThread : public concurrency::OSThread
         }
 
         switch (device.type) {
+#if __has_include(<SparkFun_MMC5983MA_Arduino_Library.h>)
         case ScanI2C::DeviceType::MMC5983MA:
             sensor = new MMC5983MASensor(device);
             break;
+#endif
         default:
             disable();
             return;
diff --git a/src/platform/nrf54l15/Arduino.h b/src/platform/nrf54l15/Arduino.h
index b608c4856..c67628afa 100644
--- a/src/platform/nrf54l15/Arduino.h
+++ b/src/platform/nrf54l15/Arduino.h
@@ -297,6 +297,7 @@ class Print
     }
 
     virtual void flush() {}
+    virtual int availableForWrite() { return 0; }
 };
 
 // ── Stream base class ────────────────────────────────────────────────────────
diff --git a/variants/nrf54l15/nrf54l15.ini b/variants/nrf54l15/nrf54l15.ini
index 31adaee10..45e997271 100644
--- a/variants/nrf54l15/nrf54l15.ini
+++ b/variants/nrf54l15/nrf54l15.ini
@@ -1,5 +1,18 @@
 [nrf54l15_base]
 platform = https://github.com/Seeed-Studio/platform-seeedboards.git
+; Pin the Zephyr package explicitly. Seeed's platform script only maps their
+; own "seeed-xiao-*" board ids to a framework-zephyr package; any other board
+; -- nrf54l15dk included -- falls back to whatever platform.json declares as
+; the default, which is now framework-zephyr-nrf54lm20 (Zephyr 4.4.0). Its
+; west manifest pulls a CMSIS_6 whose cmsis_gcc.h calls the ACLE builtins
+; __sxtb16/__sxtab16, and none of the GCC ARM toolchains PlatformIO ships
+; (8.2.1/9.2.1/9.3.1) declare them in arm_acle.h. In C that is only an
+; implicit-declaration warning, so the pure-C Zephyr core never notices; in
+; C++ it is a hard error, and any .cpp pulling in zephyr/kernel.h hits it.
+; Without the pin a fresh package cache breaks this build with nothing in the
+; tree having changed.
+platform_packages =
+  platformio/framework-zephyr-nrf54lm20@https://dl.registry.platformio.org/download/platformio/tool/framework-zephyr/3.40201.251021/framework-zephyr-3.40201.251021.tar.gz
 framework = zephyr
 extends = arduino_base