diff --git a/src/mesh/SX126xInterface.cpp b/src/mesh/SX126xInterface.cpp
index 7c46bee71..4bf9d3509 100644
--- a/src/mesh/SX126xInterface.cpp
+++ b/src/mesh/SX126xInterface.cpp
@@ -3,6 +3,7 @@
 #include "configuration.h"
 #include "error.h"
 #include "mesh/NodeDB.h"
+#include "meshUtils.h" // for pow_of_2
 #ifdef ARCH_PORTDUINO
 #include "PortduinoGlue.h"
 #endif
@@ -191,12 +192,28 @@ template <typename T> bool SX126xInterface<T>::reconfigure()
 
     // configure publicly accessible settings
     int err = lora.setSpreadingFactor(sf);
-    if (err != RADIOLIB_ERR_NONE)
-        RECORD_CRITICALERROR(meshtastic_CriticalErrorCode_INVALID_RADIO_SETTING);
+    if (err != RADIOLIB_ERR_NONE) {
+        LOG_ERROR("SX126X setSpreadingFactor(%d) at BW %.1f kHz rejected (%s%d), attempting fallback", sf, bw, radioLibErr, err);
+        for (uint8_t fallbackSf = sf - 1; fallbackSf >= 5; fallbackSf--) {
+            err = lora.setSpreadingFactor(fallbackSf);
+            if (err == RADIOLIB_ERR_NONE) {
+                LOG_WARN("SX126X fell back to SF%d at BW %.1f kHz (requested SF%d), change modem preset to match", fallbackSf, bw,
+                         sf);
+                this->sf = fallbackSf;
+                preambleTimeMsec = preambleLength * (pow_of_2(sf) / bw);
+                slotTimeMsec = computeSlotTimeMsec();
+                break;
+            }
+        }
+        if (err != RADIOLIB_ERR_NONE)
+            RECORD_CRITICALERROR(meshtastic_CriticalErrorCode_INVALID_RADIO_SETTING);
+    }
 
     err = lora.setBandwidth(bw);
-    if (err != RADIOLIB_ERR_NONE)
+    if (err != RADIOLIB_ERR_NONE) {
+        LOG_ERROR("SX126X setBandwidth(%.1f) rejected (%s%d)", bw, radioLibErr, err);
         RECORD_CRITICALERROR(meshtastic_CriticalErrorCode_INVALID_RADIO_SETTING);
+    }
 
     err = lora.setCodingRate(cr);
     if (err != RADIOLIB_ERR_NONE)
diff --git a/variants/esp32c3/diy/moonshine_ESP_C3/platformio.ini b/variants/esp32c3/diy/moonshine_ESP_C3/platformio.ini
index 314a7ae6c..217dcb111 100644
--- a/variants/esp32c3/diy/moonshine_ESP_C3/platformio.ini
+++ b/variants/esp32c3/diy/moonshine_ESP_C3/platformio.ini
@@ -8,4 +8,5 @@ build_flags =
   -D PRIVATE_HW
   -D ARDUINO_USB_MODE=1
   -D ARDUINO_USB_CDC_ON_BOOT=1
+  -D USERPREFS_LORACONFIG_MODEM_PRESET=meshtastic_Config_LoRaConfig_ModemPreset_MEDIUM_SLOW
   -I variants/esp32c3/diy/moonshine_ESP_C3
diff --git a/variants/esp32c3/diy/moonshine_ESP_C3/readme.md b/variants/esp32c3/diy/moonshine_ESP_C3/readme.md
index 8dc641ca6..545204c08 100644
--- a/variants/esp32c3/diy/moonshine_ESP_C3/readme.md
+++ b/variants/esp32c3/diy/moonshine_ESP_C3/readme.md
@@ -24,9 +24,9 @@ commenting/uncommenting the `#define` lines at the top of `variant.h`:
 
 Only one module should be enabled at a time.
 
-| Module       | Chip   | Power        | `USE_*`      | `TX_GAIN_LORA` | `SX126X_MAX_POWER` | Total output    |
-| ------------ | ------ | ------------ | ------------ | -------------- | ------------------ | --------------- |
-| E220-400M30S | LLCC68 | 30 dBm (1 W) | `USE_LLCC68` | 8              | 22                 | 22 + 8 = 30 dBm |
+| Module       | Chip   | Power        | `USE_*`      | `TX_GAIN_LORA` | `SX126X_MAX_POWER` | Total output     |
+| ------------ | ------ | ------------ | ------------ | -------------- | ------------------ | ---------------- |
+| E220-400M30S | LLCC68 | 30 dBm (1 W) | `USE_LLCC68` | 8              | 22                 | 22 + 8 = 30 dBm  |
 | E220-400M33S | LLCC68 | 33 dBm (2 W) | `USE_LLCC68` | 11             | 22                 | 22 + 11 = 33 dBm |
 | E22-400M33S  | SX1268 | 33 dBm (2 W) | `USE_SX1268` | 25             | 8                  | 8 + 25 = 33 dBm  |
 
@@ -42,21 +42,47 @@ See `variants/nrf52840/diy/moonshine_NRF52/variant.h` for the same module
 wired with a more conservative power profile (`SX126X_MAX_POWER = 2`,
 ~27 dBm output).
 
+### LLCC68 modem preset limitation
+
+The E220-400M30S and E220-400M33S use the LLCC68 chip, which does **not**
+support all spreading-factor/bandwidth combinations:
+
+| Bandwidth | Max SF |
+| --------- | ------ |
+| 125 kHz   | SF9    |
+| 250 kHz   | SF10   |
+| 500 kHz   | SF11   |
+
+SF12 is never supported on the LLCC68.
+
+The Meshtastic default preset **LongFast** (BW 250 kHz / SF11) is invalid
+for the LLCC68. This variant therefore ships with **MediumSlow**
+(BW 250 kHz / SF10) as the default preset via
+`USERPREFS_LORACONFIG_MODEM_PRESET`.
+
+If you switch to the E22-400M33S (SX1268), you can safely change the preset
+back to LongFast or any other - the SX1268 supports the full SF/BW range.
+
+**Note**: All nodes in a mesh must use the same modem preset to communicate.
+If other nodes in your network are on LongFast, either switch them to
+MediumSlow as well, or use LongTurbo (BW 500 kHz / SF11) which the LLCC68
+also supports.
+
 ## Pin map
 
-| Function      | GPIO | Notes                                  |
-| ------------- | ---- | -------------------------------------- |
-| BUTTON        | 9    | BOOT button                            |
-| LED           | 0    | Active high (`LED_STATE_ON = 1`)       |
-| BATTERY_ADC   | 1    | 0.5 divider (`ADC_MULTIPLIER = 2.0`)   |
-| LORA_RXEN     | 2    | RF switch RX enable                    |
-| LORA_DIO1     | 3    | IRQ                                    |
-| LORA_BUSY     | 4    |                                        |
-| LORA_RESET    | 5    |                                        |
-| LORA_MISO     | 6    |                                        |
-| LORA_MOSI     | 7    |                                        |
-| LORA_CS       | 8    |                                        |
-| LORA_SCK      | 10   |                                        |
+| Function    | GPIO | Notes                                |
+| ----------- | ---- | ------------------------------------ |
+| BUTTON      | 9    | BOOT button                          |
+| LED         | 0    | Active high (`LED_STATE_ON = 1`)     |
+| BATTERY_ADC | 1    | 0.5 divider (`ADC_MULTIPLIER = 2.0`) |
+| LORA_RXEN   | 2    | RF switch RX enable                  |
+| LORA_DIO1   | 3    | IRQ                                  |
+| LORA_BUSY   | 4    |                                      |
+| LORA_RESET  | 5    |                                      |
+| LORA_MISO   | 6    |                                      |
+| LORA_MOSI   | 7    |                                      |
+| LORA_CS     | 8    |                                      |
+| LORA_SCK    | 10   |                                      |
 
 DIO2 drives the module's TXEN pin internally (`SX126X_DIO2_AS_RF_SWITCH`), so
 `SX126X_TXEN` is left as `RADIOLIB_NC`. `SX126X_RXEN` is driven by GPIO2.