diff --git a/components/bootloader/project_include.cmake b/components/bootloader/project_include.cmake
index 121f6514f94..5a9448b7f28 100644
--- a/components/bootloader/project_include.cmake
+++ b/components/bootloader/project_include.cmake
@@ -76,6 +76,38 @@ if(CONFIG_SECURE_SIGNED_APPS)
             endif()
         else()
             add_custom_target(gen_secure_boot_signing_key)
+
+            # Re-run CMake if the signing key file changes, so the key type check below is re-evaluated
+            set_property(DIRECTORY APPEND PROPERTY CMAKE_CONFIGURE_DEPENDS "${secure_boot_signing_key}")
+
+            # Check that the signing key type matches the selected app signing scheme,
+            # as the signing step derives the signature type from the key itself.
+            if(CONFIG_SECURE_SIGNED_APPS_RSA_SCHEME)
+                set(key_check_args --scheme rsa)
+            elseif(CONFIG_SECURE_SIGNED_APPS_ECDSA_SCHEME)
+                set(key_check_args --scheme ecdsa_v1)
+            elseif(CONFIG_SECURE_SIGNED_APPS_ECDSA_V2_SCHEME)
+                if(CONFIG_SECURE_BOOT_ECDSA_KEY_LEN_256_BITS)
+                    set(key_check_args --scheme ecdsa_v2 --ecdsa-key-size 256)
+                elseif(CONFIG_SECURE_BOOT_ECDSA_KEY_LEN_384_BITS)
+                    set(key_check_args --scheme ecdsa_v2 --ecdsa-key-size 384)
+                else()
+                    set(key_check_args --scheme ecdsa_v2)
+                endif()
+            endif()
+
+            if(key_check_args)
+                idf_build_get_property(python PYTHON)
+                execute_process(
+                    COMMAND ${python} "${CMAKE_CURRENT_LIST_DIR}/scripts/check_secure_boot_signing_key.py"
+                            ${key_check_args} "${secure_boot_signing_key}"
+                    RESULT_VARIABLE key_check_result
+                    ERROR_VARIABLE key_check_error
+                    OUTPUT_QUIET)
+                if(NOT key_check_result EQUAL 0)
+                    message(FATAL_ERROR "CONFIG_SECURE_BOOT_SIGNING_KEY check failed: ${key_check_error}")
+                endif()
+            endif()
         endif()
 
         set(SECURE_BOOT_SIGNING_KEY ${secure_boot_signing_key}) # needed by some other components
diff --git a/components/bootloader/scripts/check_secure_boot_signing_key.py b/components/bootloader/scripts/check_secure_boot_signing_key.py
new file mode 100644
index 00000000000..002c7370318
--- /dev/null
+++ b/components/bootloader/scripts/check_secure_boot_signing_key.py
@@ -0,0 +1,92 @@
+# SPDX-FileCopyrightText: 2026 Espressif Systems (Shanghai) CO LTD
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+# Check that the Secure Boot signing key matches the selected app signing
+# scheme. The signing step (espsecure sign-data) derives the signature type
+# from the key file itself, so a mismatching key would produce an image that
+# only fails signature verification at boot.
+#
+# Invoked at configure time from components/bootloader/project_include.cmake.
+# Exits non-zero with an explanatory message on a mismatch.
+import argparse
+
+from cryptography.hazmat.primitives.asymmetric import ec
+from cryptography.hazmat.primitives.asymmetric import rsa
+from cryptography.hazmat.primitives.serialization import load_pem_private_key
+
+ECDSA_KEY_SIZE_TO_CURVE = {
+    '256': 'secp256r1',
+    '384': 'secp384r1',
+}
+
+
+def key_description(key: object) -> str:
+    if isinstance(key, rsa.RSAPrivateKey):
+        return f'an RSA {key.key_size}-bit key'
+    if isinstance(key, ec.EllipticCurvePrivateKey):
+        return f'an ECDSA key (curve {key.curve.name})'
+    return f'a {type(key).__name__} key'
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(
+        description='Check that the secure boot signing key matches the selected app signing scheme'
+    )
+    parser.add_argument(
+        '--scheme',
+        choices=['rsa', 'ecdsa_v1', 'ecdsa_v2'],
+        required=True,
+        help='App signing scheme selected in sdkconfig',
+    )
+    parser.add_argument(
+        '--ecdsa-key-size',
+        choices=sorted(ECDSA_KEY_SIZE_TO_CURVE),
+        default=None,
+        help='ECDSA key size selected in sdkconfig (ECDSA V2 scheme only)',
+    )
+    parser.add_argument('key_file', help='Path to the secure boot signing key')
+    args = parser.parse_args()
+
+    try:
+        with open(args.key_file, 'rb') as f:
+            key = load_pem_private_key(f.read(), password=None)
+    except Exception:
+        raise SystemExit(
+            f'{args.key_file} could not be parsed as a PEM private key. '
+            'Secure boot signing keys must be unencrypted PEM private keys.'
+        )
+
+    if args.scheme == 'rsa':
+        if not isinstance(key, rsa.RSAPrivateKey):
+            raise SystemExit(
+                f'{args.key_file} is {key_description(key)}, but the selected app signing scheme '
+                'requires an RSA key. Update the App Signing Scheme choice or point '
+                'CONFIG_SECURE_BOOT_SIGNING_KEY to a matching key.'
+            )
+        return
+
+    if args.scheme in ('ecdsa_v1', 'ecdsa_v2'):
+        if not isinstance(key, ec.EllipticCurvePrivateKey):
+            raise SystemExit(
+                f'{args.key_file} is {key_description(key)}, but the selected app signing scheme '
+                'requires an ECDSA key. Update the App Signing Scheme choice or point '
+                'CONFIG_SECURE_BOOT_SIGNING_KEY to a matching key.'
+            )
+
+        if args.scheme == 'ecdsa_v1':
+            expected_curve = ECDSA_KEY_SIZE_TO_CURVE['256']
+        else:
+            expected_curve = ECDSA_KEY_SIZE_TO_CURVE.get(args.ecdsa_key_size or '', '')
+
+        if expected_curve and key.curve.name != expected_curve:
+            raise SystemExit(
+                f'{args.key_file} is {key_description(key)}, but the selected app signing scheme '
+                f'requires curve {expected_curve}. Signature verification would fail at boot. '
+                'Update the ECDSA key size choice or point CONFIG_SECURE_BOOT_SIGNING_KEY to '
+                'a matching key.'
+            )
+
+
+if __name__ == '__main__':
+    main()