diff --git a/ports/esp32/boards/sdkconfig.ble b/ports/esp32/boards/sdkconfig.ble
index cdbb621a63..f714ce4629 100644
--- a/ports/esp32/boards/sdkconfig.ble
+++ b/ports/esp32/boards/sdkconfig.ble
@@ -9,9 +9,12 @@ CONFIG_BT_NIMBLE_ENABLED=y
 CONFIG_BT_NIMBLE_MAX_CONNECTIONS=4
 
 # Pin to the same core as MP.
-CONFIG_BT_NIMBLE_PINNED_TO_CORE_0=n
-CONFIG_BT_NIMBLE_PINNED_TO_CORE_1=y
-CONFIG_BT_NIMBLE_PINNED_TO_CORE=1
+# Until we move to IDF 4.2+, we need NimBLE on core 0, and for synchronisation
+# with the ringbuffer and scheduler MP needs to be on the same core.
+# See https://github.com/micropython/micropython/issues/5489
+CONFIG_BT_NIMBLE_PINNED_TO_CORE_0=y
+CONFIG_BT_NIMBLE_PINNED_TO_CORE_1=n
+CONFIG_BT_NIMBLE_PINNED_TO_CORE=0
 
 # v3.3-only (renamed in 4.0)
 CONFIG_BTDM_CONTROLLER_MODE_BLE_ONLY=y
diff --git a/ports/esp32/mphalport.h b/ports/esp32/mphalport.h
index 1f78d820a3..60cc308d68 100644
--- a/ports/esp32/mphalport.h
+++ b/ports/esp32/mphalport.h
@@ -35,8 +35,11 @@
 #include "freertos/FreeRTOS.h"
 #include "freertos/task.h"
 
-// The core that the MicroPython task(s) are pinned to
-#define MP_TASK_COREID (1)
+// The core that the MicroPython task(s) are pinned to.
+// Until we move to IDF 4.2+, we need NimBLE on core 0, and for synchronisation
+// with the ringbuffer and scheduler MP needs to be on the same core.
+// See https://github.com/micropython/micropython/issues/5489
+#define MP_TASK_COREID (0)
 
 extern TaskHandle_t mp_main_task_handle;