diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index a7c7cf99a..3f6458285 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -278,6 +278,7 @@ jobs:
       matrix:
         toolchain:
           - 'arm-gcc'
+          - 'riscv-gcc'
           - 'esp-idf'
     with:
       build-system: 'cmake'
diff --git a/test/hil/hil_ci_set_matrix.py b/test/hil/hil_ci_set_matrix.py
index baa24afb1..13f7f1882 100644
--- a/test/hil/hil_ci_set_matrix.py
+++ b/test/hil/hil_ci_set_matrix.py
@@ -19,8 +19,12 @@ def main():
     parser.add_argument('config_files', nargs='+', help='Configuration JSON file(s)')
     args = parser.parse_args()
 
+    # Toolchain buckets must match the toolchains instantiated by the hil-build
+    # job in .github/workflows/build.yml. Keep all keys present (even if empty)
+    # so `fromJSON(hil_json)[toolchain]` always resolves to a list.
     matrix = {
         'arm-gcc': [],
+        'riscv-gcc': [],
         'esp-idf': []
     }
 
@@ -38,22 +42,28 @@ def main():
         for board in config['boards']:
             name = board['name']
             flasher = board['flasher']
+            # esptool boards must build under esp-idf; others default to arm-gcc
+            # but may opt into another bucket via an explicit "toolchain" field
+            # (e.g. RISC-V boards like ch32v20x need "riscv-gcc").
             if flasher['name'] == 'esptool':
                 toolchain = 'esp-idf'
             else:
-                toolchain = 'arm-gcc'
+                toolchain = board.get('toolchain', 'arm-gcc')
 
             build_board = f'-b {name}'
             if 'build' in board and 'args' in board['build']:
                 build_board += ' ' + ' '.join(f'-D{a}' for a in board['build']['args'])
 
-            # Each variant builds into cmake-build-<variant.name> with its raw CFLAGS.
-            # No 'variant' -> a single build named after the board.
+            # Each variant builds into cmake-build-<variant.name> with its own cmake
+            # -D defines and raw CFLAGS. No 'variant' -> a single build named after
+            # the board.
             variants = board.get('variant') or [{'name': name, 'flags': ''}]
             for v in variants:
                 arg = build_board
                 if v['name'] != name:
                     arg += f' --build-name {v["name"]}'
+                for d in v.get('defines', []):
+                    arg += f' -D{d}'
                 for tok in v.get('flags', '').split():
                     arg += f' --cflag={tok}'
                 append_build_arg(toolchain, arg)
diff --git a/test/hil/hil_test.py b/test/hil/hil_test.py
index da13fcbaf..fb9a8205c 100755
--- a/test/hil/hil_test.py
+++ b/test/hil/hil_test.py
@@ -126,8 +126,9 @@ class BuildCfg(TypedDict, total=False):
 
 
 class VariantCfg(TypedDict, total=False):
-    name: str   # build dir (cmake-build-<name>) and HIL report row
-    flags: str  # raw CFLAGS, e.g. "-DCFG_TUD_DWC2_DMA_ENABLE=1"
+    name: str           # build dir (cmake-build-<name>) and HIL report row
+    flags: str          # raw CFLAGS, e.g. "-DCFG_TUD_DWC2_DMA_ENABLE=1"
+    defines: list[str]  # cmake -D defines, e.g. ["RHPORT_DEVICE=1"] (vs flags which are compiler-only)
 
 
 class Board(TypedDict):
@@ -137,6 +138,7 @@ class Board(TypedDict):
     flasher: FlasherCfg
     build: NotRequired[BuildCfg]
     variant: NotRequired[list[VariantCfg]]
+    toolchain: NotRequired[str]  # CI build bucket override, e.g. "riscv-gcc" (consumed by hil_ci_set_matrix.py)
 
 
 class HilConfig(TypedDict):
@@ -1634,6 +1636,8 @@ def build_board(board: Board) -> tuple[str, int]:
             cmd += ['-D', d]
         if v['name'] != name:
             cmd += ['--build-name', v['name']]
+        for d in v.get('defines', []):
+            cmd += ['-D', d]
         for tok in v.get('flags', '').split():
             cmd += [f'--cflag={tok}']
         if verbose:
diff --git a/test/hil/tinyusb.json b/test/hil/tinyusb.json
index afe3c4d03..ea9342c03 100644
--- a/test/hil/tinyusb.json
+++ b/test/hil/tinyusb.json
@@ -458,6 +458,25 @@
                 "name": "stlink",
                 "uid": "0668FF575457657187061314"
             }
+        },
+        {
+            "name": "nanoch32v203",
+            "uid": "CDAB277B0FBC03E339E339E3",
+            "toolchain": "riscv-gcc",
+            "variant": [
+                {"name": "nanoch32v203-fsdev", "defines": ["RHPORT_DEVICE=0"]},
+                {"name": "nanoch32v203-usbfs", "defines": ["RHPORT_DEVICE=1"]}
+            ],
+            "tests": {
+                "device": true,
+                "host": false,
+                "dual": false
+            },
+            "flasher": {
+                "name": "openocd_wch",
+                "uid": "EBCA8F0670AF",
+                "args": ""
+            }
         }
     ],
     "boards-skip": [
@@ -478,20 +497,6 @@
                 "uid": "000778170924",
                 "args": "-device stm32f769ni"
             }
-        },
-        {
-            "name": "nanoch32v203",
-            "uid": "CDAB277B0FBC03E339E339E3",
-            "tests": {
-                "device": true,
-                "host": false,
-                "dual": false
-            },
-            "flasher": {
-                "name": "openocd_wch",
-                "uid": "EBCA8F0670AF",
-                "args": ""
-            }
         }
     ]
 }