diff --git a/.github/workflows/build.yaml b/.github/workflows/build.yaml
index 7ef5508..d4b1f33 100644
--- a/.github/workflows/build.yaml
+++ b/.github/workflows/build.yaml
@@ -60,9 +60,7 @@ jobs:
         # fwname: firmware-only binary for OTA updates
         # obname: onboard image (bootloader + partitions + firmware + littlefs merged)
         #         for flashing a new chip via USB/serial
-        # addr_bootloader: chip-dependent (ESP32: 0x1000, S3/C6: 0x0)
-        # No C3: on ESP-IDF 5.5 its image no longer fits the 1.5 MB OTA slot
-        # (docs/adr/0003-pioarduino-idf55.md).  C3 boards stay on 3.0.x.
+        # addr_bootloader: chip-dependent (ESP32: 0x1000, S3/C3/C6: 0x0)
         # addr_fs: must match spiffs/littlefs offset in esp32_3MB.csv
         include:
           - env: esp32dev
@@ -81,6 +79,14 @@ jobs:
             fwname: SomfyController.ino.esp32s3.bin
             fsname: SomfyController.littlefs.esp32s3.bin
             obname: SomfyController.onboard.esp32s3.bin
+          - env: esp32c3
+            name: ESP32-C3
+            chip: ESP32-C3
+            addr_bootloader: "0x0"
+            addr_fs: "0x310000"
+            fwname: SomfyController.ino.esp32c3.bin
+            fsname: SomfyController.littlefs.esp32c3.bin
+            obname: SomfyController.onboard.esp32c3.bin
           - env: esp32c6
             name: ESP32-C6
             chip: ESP32-C6
diff --git a/docs/adr/0003-pioarduino-idf55.md b/docs/adr/0003-pioarduino-idf55.md
index 3a6baf0..96fbc8b 100644
--- a/docs/adr/0003-pioarduino-idf55.md
+++ b/docs/adr/0003-pioarduino-idf55.md
@@ -12,7 +12,9 @@ We moved every firmware env from `espressif32 @ 6.13.0` (Arduino 2.0.17 on ESP-I
 
 - **Firmware size.** The ESP32 image grows from 1,382,640 bytes (v3.0.14) to 1,555,472 at `CORE_DEBUG_LEVEL=2`, leaving 17 KB of the 1.5 MB OTA slot. At level 3 it doesn't fit, so release envs build at level 2 (warnings and errors) and debug envs stay at 3. PlatformIO's "Flash:" figure counts ELF sections, not the image, and reads about 45 KB low, so CI checks `firmware.bin` against the app partition and fails under 8 KB free (`.github/size_check.py`).
 - **No more C3 builds.** Its image grows by 214 KB to 1,651,216 bytes, 76.5 KB over the OTA slot even at level 2. C3 boards stay on the 3.0.x releases.
+
+  > **Amended by [ADR 0006](0006-two-security-modes-eleven-http-routes.md) (4.0.0).** The C3 builds again. Without the old API (ports 8080 and 8081), its image is 1,498,512 bytes at level 2 and leaves 72.6 KB of the OTA slot. It runs on chip revision v0.3 or later only: the framework's C3 libraries are built with `CONFIG_ESP32C3_REV_MIN_3`. Its default radio pins moved off GPIO 12-17, which hold the SPI flash.
 - **Ethernet PHY ids are ours.** Arduino 3.x renumbered `eth_phy_type_t` (`ETH_PHY_GENERIC` is 0). NVS, backups and the web UI keep the Arduino 2.x numbers as `eth_phy_id_t` (`src/EthPhy.h`), translated by name when Ethernet starts. Never cast a stored id to the framework enum.
-- **Ethernet only on the original ESP32.** Arduino 3.x has the RMII MAC API only where `CONFIG_ETH_USE_ESP32_EMAC` is set. S3 and C6 build without Ethernet.
+- **Ethernet only on the original ESP32.** Arduino 3.x has the RMII MAC API only where `CONFIG_ETH_USE_ESP32_EMAC` is set. S3, C3 and C6 build without Ethernet.
 - **Updates roll back until proven.** We override the core's `verifyRollbackLater()` hook to return true, and `loop()` marks the new firmware valid once it has run 60 s and the network is up. A reset before then boots the previous firmware. The LittleFS image an update wrote stays, so the old firmware runs with the new web UI.
 - **Tooling.** pioarduino needs its own Core fork (`pip install pioarduino`, the pioarduino IDE extension in VS Code), which it installs into `~/.platformio/penv` in place of PlatformIO Core.
diff --git a/platformio.ini b/platformio.ini
index e7e5b60..aaed9a4 100644
--- a/platformio.ini
+++ b/platformio.ini
@@ -95,6 +95,14 @@ build_flags =
 	${dualcore.build_flags}
 	-DCORE_DEBUG_LEVEL=2
 
+[env:esp32c3]
+extends = esp32
+board = esp32-c3-devkitm-1
+board_build.partitions = esp32_3MB.csv
+build_flags =
+	${esp32.build_flags}
+	-DCORE_DEBUG_LEVEL=2
+
 ; Released as a debug build with one 3 MB app slot, so C6 boards update over
 ; USB, not OTA.
 [env:esp32c6]
diff --git a/src/Transceiver.cpp b/src/Transceiver.cpp
index 9f10d2b..48ca4cf 100644
--- a/src/Transceiver.cpp
+++ b/src/Transceiver.cpp
@@ -474,12 +474,14 @@ void transceiver_config_t::load() {
         this->CSNPin = 34;
         break;
       case esp_chip_model_t::CHIP_ESP32C3:
-        this->TXPin = 13;
-        this->RXPin = 12;
-        this->MOSIPin = 16;
-        this->MISOPin = 17;
-        this->SCKPin = 15;
-        this->CSNPin = 14;
+        // The framework's default SPI pins (variants/esp32c3).  12-17 hold the
+        // SPI flash, and 2, 8 and 9 are strapping pins.
+        this->TXPin = 10;
+        this->RXPin = 3;
+        this->MOSIPin = 6;
+        this->MISOPin = 5;
+        this->SCKPin = 4;
+        this->CSNPin = 7;
         break;
 #ifdef CONFIG_IDF_TARGET_ESP32C6
       case esp_chip_model_t::CHIP_ESP32C6:
diff --git a/test/test_utils/test_utils.cpp b/test/test_utils/test_utils.cpp
index 7b8bfba..040d34f 100644
--- a/test/test_utils/test_utils.cpp
+++ b/test/test_utils/test_utils.cpp
@@ -278,14 +278,10 @@ static void test_releaseAssetName_matches_the_release_workflow() {
   TEST_ASSERT_EQUAL_STRING("SomfyController.ino.esp32.bin", buf);
   releaseAssetName(buf, sizeof(buf), "littlefs", "s3");
   TEST_ASSERT_EQUAL_STRING("SomfyController.littlefs.esp32s3.bin", buf);
-  releaseAssetName(buf, sizeof(buf), "littlefs", "c6");
-  TEST_ASSERT_EQUAL_STRING("SomfyController.littlefs.esp32c6.bin", buf);
-}
-static void test_releaseAssetName_keeps_c3() {
-  // C3 is out of the IDF 5.5 builds for now (ADR 0003) but is coming back.
-  char buf[64];
   releaseAssetName(buf, sizeof(buf), "ino", "c3");
   TEST_ASSERT_EQUAL_STRING("SomfyController.ino.esp32c3.bin", buf);
+  releaseAssetName(buf, sizeof(buf), "littlefs", "c6");
+  TEST_ASSERT_EQUAL_STRING("SomfyController.littlefs.esp32c6.bin", buf);
 }
 
 /*********************************************************************
@@ -432,7 +428,6 @@ int main(int argc, char **argv) {
   RUN_TEST(test_otaProven_not_before_the_minimum_uptime);
   RUN_TEST(test_otaProven_not_without_network);
   RUN_TEST(test_releaseAssetName_matches_the_release_workflow);
-  RUN_TEST(test_releaseAssetName_keeps_c3);
   RUN_TEST(test_formatBacktrace_frames_the_dump_holds);
   RUN_TEST(test_formatBacktrace_garbage_depth_stays_in_bounds);
   RUN_TEST(test_formatBacktrace_stops_when_the_buffer_is_full);