diff --git a/tests/scripts/generate_psa_tests.py b/tests/scripts/generate_psa_tests.py
index 933dd0a..8e81675 100755
--- a/tests/scripts/generate_psa_tests.py
+++ b/tests/scripts/generate_psa_tests.py
@@ -539,6 +539,9 @@
         # loss of test coverage.
         if key_type.string == 'PSA_KEY_TYPE_RAW_DATA':
             return False
+        # Mbed TLS only supports 128-bit keys for RC4.
+        if key_type.string == 'PSA_KEY_TYPE_ARC4' and bits != 128:
+            return False
         # OAEP requires room for two hashes plus wrapping
         m = cls.RSA_OAEP_RE.match(alg.string)
         if m:
diff --git a/tests/suites/test_suite_psa_crypto_op_fail.misc.data b/tests/suites/test_suite_psa_crypto_op_fail.misc.data
index 147c3b7..b25053d 100644
--- a/tests/suites/test_suite_psa_crypto_op_fail.misc.data
+++ b/tests/suites/test_suite_psa_crypto_op_fail.misc.data
@@ -1,15 +1,39 @@
 # Most operation failure test cases are automatically generated in
 # test_suite_psa_crypto_op_fail.generated.data. The manually written
-# test cases in this file are only intended to help with debugging the
-# test code.
+# test cases in this file cover some edge cases, plus a few to help with
+# with debugging the test code.
 
+# Redundant, to help debugging the test code
 PSA hash: invalid algorithm
 hash_fail:PSA_ALG_ECDSA_ANY:PSA_ERROR_INVALID_ARGUMENT
 
+# For RC4, Mbed TLS only supports 128-bit keys. PSA allows 40 to 2048 bits.
+# The RC4 construction allows any whole number of bytes from 1 to 256 bytes
+# (8 to 2048 bits).
+PSA cipher STREAM_CIPHER: 8-bit ARC4 never supported
+cipher_fail:PSA_KEY_TYPE_ARC4:"41":PSA_ALG_STREAM_CIPHER:PSA_ERROR_NOT_SUPPORTED
+
+PSA cipher STREAM_CIPHER: 40-bit ARC4 never supported
+cipher_fail:PSA_KEY_TYPE_ARC4:"4152433420":PSA_ALG_STREAM_CIPHER:PSA_ERROR_NOT_SUPPORTED
+
+PSA cipher STREAM_CIPHER: 120-bit ARC4 never supported
+cipher_fail:PSA_KEY_TYPE_ARC4:"41524334206b657941524334206b65":PSA_ALG_STREAM_CIPHER:PSA_ERROR_NOT_SUPPORTED
+
+PSA cipher STREAM_CIPHER: 136-bit ARC4 never supported
+cipher_fail:PSA_KEY_TYPE_ARC4:"41524334206b657941524334206b657941":PSA_ALG_STREAM_CIPHER:PSA_ERROR_NOT_SUPPORTED
+
+PSA cipher STREAM_CIPHER: 256-bit ARC4 never supported
+cipher_fail:PSA_KEY_TYPE_ARC4:"41524334206b657941524334206b657941524334206b657941524334206b6579":PSA_ALG_STREAM_CIPHER:PSA_ERROR_NOT_SUPPORTED
+
+PSA cipher STREAM_CIPHER: 2048-bit ARC4 never supported
+cipher_fail:PSA_KEY_TYPE_ARC4:"41524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b657941524334206b6579":PSA_ALG_STREAM_CIPHER:PSA_ERROR_NOT_SUPPORTED
+
+# Redundant, to help debugging the test code
 PSA sign RSA_PSS(SHA_256): incompatible key type
 depends_on:PSA_WANT_ALG_RSA_PSS:PSA_WANT_ALG_SHA_256:PSA_WANT_KEY_TYPE_AES
 sign_fail:PSA_KEY_TYPE_AES:"48657265006973206b6579a064617461":PSA_ALG_RSA_PSS(PSA_ALG_SHA_256):0:PSA_ERROR_INVALID_ARGUMENT
 
+# Redundant, to help debugging the test code
 PSA sign RSA_PSS(SHA_256): RSA_PSS not enabled, key pair
 depends_on:!PSA_WANT_ALG_RSA_PSS:PSA_WANT_ALG_SHA_256:PSA_WANT_KEY_TYPE_RSA_KEY_PAIR
 sign_fail:PSA_KEY_TYPE_RSA_KEY_PAIR:"3082025e02010002818100af057d396ee84fb75fdbb5c2b13c7fe5a654aa8aa2470b541ee1feb0b12d25c79711531249e1129628042dbbb6c120d1443524ef4c0e6e1d8956eeb2077af12349ddeee54483bc06c2c61948cd02b202e796aebd94d3a7cbf859c2c1819c324cb82b9cd34ede263a2abffe4733f077869e8660f7d6834da53d690ef7985f6bc3020301000102818100874bf0ffc2f2a71d14671ddd0171c954d7fdbf50281e4f6d99ea0e1ebcf82faa58e7b595ffb293d1abe17f110b37c48cc0f36c37e84d876621d327f64bbe08457d3ec4098ba2fa0a319fba411c2841ed7be83196a8cdf9daa5d00694bc335fc4c32217fe0488bce9cb7202e59468b1ead119000477db2ca797fac19eda3f58c1024100e2ab760841bb9d30a81d222de1eb7381d82214407f1b975cbbfe4e1a9467fd98adbd78f607836ca5be1928b9d160d97fd45c12d6b52e2c9871a174c66b488113024100c5ab27602159ae7d6f20c3c2ee851e46dc112e689e28d5fcbbf990a99ef8a90b8bb44fd36467e7fc1789ceb663abda338652c3c73f111774902e840565927091024100b6cdbd354f7df579a63b48b3643e353b84898777b48b15f94e0bfc0567a6ae5911d57ad6409cf7647bf96264e9bd87eb95e263b7110b9a1f9f94acced0fafa4d024071195eec37e8d257decfc672b07ae639f10cbb9b0c739d0c809968d644a94e3fd6ed9287077a14583f379058f76a8aecd43c62dc8c0f41766650d725275ac4a1024100bb32d133edc2e048d463388b7be9cb4be29f4b6250be603e70e3647501c97ddde20a4e71be95fd5e71784e25aca4baf25be5738aae59bbfe1c997781447a2b24":PSA_ALG_RSA_PSS(PSA_ALG_SHA_256):0:PSA_ERROR_NOT_SUPPORTED
diff --git a/tests/suites/test_suite_psa_crypto_storage_format.v0.data b/tests/suites/test_suite_psa_crypto_storage_format.v0.data
index fd38738..0be1066 100644
--- a/tests/suites/test_suite_psa_crypto_storage_format.v0.data
+++ b/tests/suites/test_suite_psa_crypto_storage_format.v0.data
@@ -406,11 +406,11 @@
 
 read type: ARC4 8-bit
 depends_on:PSA_WANT_KEY_TYPE_ARC4
-key_storage_read:0x0001:PSA_KEY_TYPE_ARC4:8:PSA_KEY_USAGE_EXPORT:0x0000:0x0000:"48":"505341004b4559000000000001000000022008000100000000000000000000000100000048":TEST_FLAG_EXERCISE
+key_storage_read:0x0001:PSA_KEY_TYPE_ARC4:8:PSA_KEY_USAGE_EXPORT:0x0000:0x0000:"48":"505341004b4559000000000001000000022008000100000000000000000000000100000048":0
 
 read type: ARC4 8-bit, STREAM_CIPHER
 depends_on:PSA_WANT_ALG_STREAM_CIPHER:PSA_WANT_KEY_TYPE_ARC4
-key_storage_read:0x0001:PSA_KEY_TYPE_ARC4:8:PSA_KEY_USAGE_DECRYPT | PSA_KEY_USAGE_ENCRYPT | PSA_KEY_USAGE_EXPORT:PSA_ALG_STREAM_CIPHER:0x0000:"48":"505341004b4559000000000001000000022008000103000000018004000000000100000048":TEST_FLAG_EXERCISE
+key_storage_read:0x0001:PSA_KEY_TYPE_ARC4:8:PSA_KEY_USAGE_DECRYPT | PSA_KEY_USAGE_ENCRYPT | PSA_KEY_USAGE_EXPORT:PSA_ALG_STREAM_CIPHER:0x0000:"48":"505341004b4559000000000001000000022008000103000000018004000000000100000048":0
 
 read type: ARC4 128-bit
 depends_on:PSA_WANT_KEY_TYPE_ARC4
@@ -422,11 +422,11 @@
 
 read type: ARC4 2048-bit
 depends_on:PSA_WANT_KEY_TYPE_ARC4
-key_storage_read:0x0001:PSA_KEY_TYPE_ARC4:2048:PSA_KEY_USAGE_EXPORT:0x0000:0x0000:"48657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a064617461":"505341004b4559000000000001000000022000080100000000000000000000000001000048657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a064617461":TEST_FLAG_EXERCISE
+key_storage_read:0x0001:PSA_KEY_TYPE_ARC4:2048:PSA_KEY_USAGE_EXPORT:0x0000:0x0000:"48657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a064617461":"505341004b4559000000000001000000022000080100000000000000000000000001000048657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a064617461":0
 
 read type: ARC4 2048-bit, STREAM_CIPHER
 depends_on:PSA_WANT_ALG_STREAM_CIPHER:PSA_WANT_KEY_TYPE_ARC4
-key_storage_read:0x0001:PSA_KEY_TYPE_ARC4:2048:PSA_KEY_USAGE_DECRYPT | PSA_KEY_USAGE_ENCRYPT | PSA_KEY_USAGE_EXPORT:PSA_ALG_STREAM_CIPHER:0x0000:"48657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a064617461":"505341004b4559000000000001000000022000080103000000018004000000000001000048657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a064617461":TEST_FLAG_EXERCISE
+key_storage_read:0x0001:PSA_KEY_TYPE_ARC4:2048:PSA_KEY_USAGE_DECRYPT | PSA_KEY_USAGE_ENCRYPT | PSA_KEY_USAGE_EXPORT:PSA_ALG_STREAM_CIPHER:0x0000:"48657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a064617461":"505341004b4559000000000001000000022000080103000000018004000000000001000048657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a06461746148657265006973206b6579a064617461":0
 
 read type: ARIA 128-bit
 depends_on:PSA_WANT_KEY_TYPE_ARIA