diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 4b4d14b..ef8a16c 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -31,13 +31,23 @@ jobs:
         run: make test
 
   esp-idf:
-    name: ESP-IDF component build
+    name: ESP-IDF ${{ matrix.idf }} build (${{ matrix.target }})
     runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        # v5.5.x uses plain mbedtls; v6.x (mbedTLS v4) exercises the
+        # mbedtls_compat shim path. esp32p4 is Kern's target on IDF 6.
+        include:
+          - idf: v5.5.4
+            target: esp32
+          - idf: v6.0.2
+            target: esp32p4
     steps:
       - uses: actions/checkout@v4
-      - name: Build smoke-test app for esp32
+      - name: Build smoke-test app
         uses: espressif/esp-idf-ci-action@v1
         with:
-          esp_idf_version: v5.5.4
-          target: esp32
+          esp_idf_version: ${{ matrix.idf }}
+          target: ${{ matrix.target }}
           path: 'tests/esp-idf-smoke'
diff --git a/tests/esp-idf-smoke/components/cUR/CMakeLists.txt b/tests/esp-idf-smoke/components/cUR/CMakeLists.txt
index c41f271..4c0573e 100644
--- a/tests/esp-idf-smoke/components/cUR/CMakeLists.txt
+++ b/tests/esp-idf-smoke/components/cUR/CMakeLists.txt
@@ -11,10 +11,19 @@ file(GLOB CUR_SRCS
     "${CUR_REPO_ROOT}/src/types/*.c"
 )
 
+# Mirror the repo-root CMakeLists.txt: mbedTLS v4 (ESP-IDF >= 6.0) needs the
+# mbedtls_compat header shim (vendored next to this component for the smoke
+# build; real consumers like Kern bring their own).
+if(IDF_VERSION_MAJOR GREATER_EQUAL 6)
+    set(CUR_SMOKE_REQUIRES mbedtls mbedtls_compat)
+else()
+    set(CUR_SMOKE_REQUIRES mbedtls)
+endif()
+
 idf_component_register(
     SRCS ${CUR_SRCS}
     INCLUDE_DIRS "${CUR_REPO_ROOT}/src"
-    REQUIRES mbedtls
+    REQUIRES ${CUR_SMOKE_REQUIRES}
 )
 
 target_compile_definitions(${COMPONENT_LIB} PUBLIC UR_USE_MBEDTLS_SHA256)
diff --git a/tests/esp-idf-smoke/components/mbedtls_compat/CMakeLists.txt b/tests/esp-idf-smoke/components/mbedtls_compat/CMakeLists.txt
new file mode 100644
index 0000000..bf60e76
--- /dev/null
+++ b/tests/esp-idf-smoke/components/mbedtls_compat/CMakeLists.txt
@@ -0,0 +1,10 @@
+# Minimal vendored copy of the Kern project's mbedtls_compat shim, trimmed
+# to SHA-256 (the only mbedTLS API cUR uses). mbedTLS v4 (ESP-IDF >= 6.0)
+# moved the crypto headers from mbedtls/ to mbedtls/private/; this
+# header-only component redirects #include <mbedtls/sha256.h> so
+# src/sha256/sha256_compat.h keeps working. Real consumers on IDF >= 6
+# (e.g. Kern) provide their own copy — see the repo-root CMakeLists.txt.
+idf_component_register(
+    INCLUDE_DIRS "."
+    REQUIRES mbedtls
+)
diff --git a/tests/esp-idf-smoke/components/mbedtls_compat/mbedtls/sha256.h b/tests/esp-idf-smoke/components/mbedtls_compat/mbedtls/sha256.h
new file mode 100644
index 0000000..a313b12
--- /dev/null
+++ b/tests/esp-idf-smoke/components/mbedtls_compat/mbedtls/sha256.h
@@ -0,0 +1,5 @@
+// Compatibility shim (vendored from Kern): mbedTLS v4 moved sha256.h to
+// mbedtls/private/. MBEDTLS_ALLOW_PRIVATE_ACCESS keeps the context struct
+// fields reachable through the private header.
+#define MBEDTLS_ALLOW_PRIVATE_ACCESS
+#include "mbedtls/private/sha256.h"
diff --git a/uUR.c b/uUR.c
index c2714f8..d3fd9e3 100644
--- a/uUR.c
+++ b/uUR.c
@@ -1026,8 +1026,18 @@ const mp_obj_module_t bc_ur_module = {
 // legacy form and fail to compile. MICROPY_VERSION is
 // (major << 16 | minor << 8 | micro); on builds too old to define it, the
 // expression evaluates to 0 and correctly selects the legacy 3-arg form.
+//
+// The modern branch registers through the UR_REGISTER_MODULE alias, not the
+// macro's own name: the legacy MaixPy (K210) build generates
+// genhdr/moduledefs.h by regex-scanning the RAW source for the macro name,
+// ignoring preprocessor conditionals, and with two visible registrations the
+// scan mangles the generated header ("#else after #else"). The alias keeps
+// the modern line invisible to that scanner; modern builds collect
+// registrations from PREPROCESSED source, where the alias has already
+// expanded to the real macro.
 #if MICROPY_VERSION >= ((1 << 16) | (19 << 8)) // >= v1.19
-MP_REGISTER_MODULE(MP_QSTR_uUR, bc_ur_module);
+#define UR_REGISTER_MODULE MP_REGISTER_MODULE
+UR_REGISTER_MODULE(MP_QSTR_uUR, bc_ur_module);
 #else
 MP_REGISTER_MODULE(MP_QSTR_uUR, bc_ur_module, MODULE_BC_UR_ENABLED);
 #endif