diff --git a/variants/nrf52840/nrf52.ini b/variants/nrf52840/nrf52.ini
index d4249bb78..471db3c8d 100644
--- a/variants/nrf52840/nrf52.ini
+++ b/variants/nrf52840/nrf52.ini
@@ -30,6 +30,13 @@ build_flags =
   ; 2048 words = 8 KB, validated on hardware. Value is in WORDS; requires the #ifndef guard
   ; from meshtastic/Adafruit_nRF52_Arduino#7 (harmless redefinition warning until it merges).
   -DLOOP_STACK_SZ=2048
+  ; The Bluefruit BLE task runs the ENTIRE phone-API chain inline (toRadioWriteCb ->
+  ; handleToRadio -> admin set-config -> radio reconfigure -> LittleFS save): its stock
+  ; 5 KB (1280-word) stack overflows during pairing/first-sync, resetting mid-flash-write
+  ; and tearing LittleFS (auto-format -> total config/key wipe, critical fault #13).
+  ; Reproduced on Wio Tracker L1 @ develop 6908d27. Same rationale as LOOP_STACK_SZ above;
+  ; bluefruit.cpp's #ifndef guard makes the -D take effect without a framework patch.
+  -DCFG_BLE_TASK_STACKSIZE=2048
   -DLFS_NO_ASSERT                      ; Disable LFS assertions , see https://github.com/meshtastic/firmware/pull/3818
   -DMESHTASTIC_EXCLUDE_AUDIO=1
   -DMESHTASTIC_EXCLUDE_PAXCOUNTER=1