diff --git a/dlls/crypt32/tests/msg.c b/dlls/crypt32/tests/msg.c
index d2d94888b97..250ac9f9986 100644
--- a/dlls/crypt32/tests/msg.c
+++ b/dlls/crypt32/tests/msg.c
@@ -1061,9 +1061,125 @@ static void test_signed_msg_open(void)
      PROV_RSA_FULL, CRYPT_DELETEKEYSET);
 }
 
+static const BYTE privKey[] = {
+ 0x07, 0x02, 0x00, 0x00, 0x00, 0x24, 0x00, 0x00, 0x52, 0x53, 0x41, 0x32, 0x00,
+ 0x02, 0x00, 0x00, 0x01, 0x00, 0x01, 0x00, 0x79, 0x10, 0x1c, 0xd0, 0x6b, 0x10,
+ 0x18, 0x30, 0x94, 0x61, 0xdc, 0x0e, 0xcb, 0x96, 0x4e, 0x21, 0x3f, 0x79, 0xcd,
+ 0xa9, 0x17, 0x62, 0xbc, 0xbb, 0x61, 0x4c, 0xe0, 0x75, 0x38, 0x6c, 0xf3, 0xde,
+ 0x60, 0x86, 0x03, 0x97, 0x65, 0xeb, 0x1e, 0x6b, 0xdb, 0x53, 0x85, 0xad, 0x68,
+ 0x21, 0xf1, 0x5d, 0xe7, 0x1f, 0xe6, 0x53, 0xb4, 0xbb, 0x59, 0x3e, 0x14, 0x27,
+ 0xb1, 0x83, 0xa7, 0x3a, 0x54, 0xe2, 0x8f, 0x65, 0x8e, 0x6a, 0x4a, 0xcf, 0x3b,
+ 0x1f, 0x65, 0xff, 0xfe, 0xf1, 0x31, 0x3a, 0x37, 0x7a, 0x8b, 0xcb, 0xc6, 0xd4,
+ 0x98, 0x50, 0x36, 0x67, 0xe4, 0xa1, 0xe8, 0x7e, 0x8a, 0xc5, 0x23, 0xf2, 0x77,
+ 0xf5, 0x37, 0x61, 0x49, 0x72, 0x59, 0xe8, 0x3d, 0xf7, 0x60, 0xb2, 0x77, 0xca,
+ 0x78, 0x54, 0x6d, 0x65, 0x9e, 0x03, 0x97, 0x1b, 0x61, 0xbd, 0x0c, 0xd8, 0x06,
+ 0x63, 0xe2, 0xc5, 0x48, 0xef, 0xb3, 0xe2, 0x6e, 0x98, 0x7d, 0xbd, 0x4e, 0x72,
+ 0x91, 0xdb, 0x31, 0x57, 0xe3, 0x65, 0x3a, 0x49, 0xca, 0xec, 0xd2, 0x02, 0x4e,
+ 0x22, 0x7e, 0x72, 0x8e, 0xf9, 0x79, 0x84, 0x82, 0xdf, 0x7b, 0x92, 0x2d, 0xaf,
+ 0xc9, 0xe4, 0x33, 0xef, 0x89, 0x5c, 0x66, 0x99, 0xd8, 0x80, 0x81, 0x47, 0x2b,
+ 0xb1, 0x66, 0x02, 0x84, 0x59, 0x7b, 0xc3, 0xbe, 0x98, 0x45, 0x4a, 0x3d, 0xdd,
+ 0xea, 0x2b, 0xdf, 0x4e, 0xb4, 0x24, 0x6b, 0xec, 0xe7, 0xd9, 0x0c, 0x45, 0xb8,
+ 0xbe, 0xca, 0x69, 0x37, 0x92, 0x4c, 0x38, 0x6b, 0x96, 0x6d, 0xcd, 0x86, 0x67,
+ 0x5c, 0xea, 0x54, 0x94, 0xa4, 0xca, 0xa4, 0x02, 0xa5, 0x21, 0x4d, 0xae, 0x40,
+ 0x8f, 0x9d, 0x51, 0x83, 0xf2, 0x3f, 0x33, 0xc1, 0x72, 0xb4, 0x1d, 0x94, 0x6e,
+ 0x7d, 0xe4, 0x27, 0x3f, 0xea, 0xff, 0xe5, 0x9b, 0xa7, 0x5e, 0x55, 0x8e, 0x0d,
+ 0x69, 0x1c, 0x7a, 0xff, 0x81, 0x9d, 0x53, 0x52, 0x97, 0x9a, 0x76, 0x79, 0xda,
+ 0x93, 0x32, 0x16, 0xec, 0x69, 0x51, 0x1a, 0x4e, 0xc3, 0xf1, 0x72, 0x80, 0x78,
+ 0x5e, 0x66, 0x4a, 0x8d, 0x85, 0x2f, 0x3f, 0xb2, 0xa7 };
+
+static void test_signed_msg_update(void)
+{
+    HCRYPTMSG msg;
+    BOOL ret;
+    CMSG_SIGNED_ENCODE_INFO signInfo = { sizeof(signInfo), 0 };
+    CMSG_SIGNER_ENCODE_INFO signer = { sizeof(signer), 0 };
+    CERT_INFO certInfo = { 0 };
+    HCRYPTKEY key;
+    char oid_rsa_md5[] = szOID_RSA_MD5;
+
+    certInfo.SerialNumber.cbData = sizeof(serialNum);
+    certInfo.SerialNumber.pbData = serialNum;
+    certInfo.Issuer.cbData = sizeof(encodedCommonName);
+    certInfo.Issuer.pbData = encodedCommonName;
+    signer.pCertInfo = &certInfo;
+    signer.HashAlgorithm.pszObjId = oid_rsa_md5;
+    signInfo.cSigners = 1;
+    signInfo.rgSigners = &signer;
+    ret = CryptAcquireContextW(&signer.hCryptProv, cspNameW, NULL,
+     PROV_RSA_FULL, CRYPT_NEWKEYSET);
+    if (!ret && GetLastError() == NTE_EXISTS)
+        ret = CryptAcquireContextW(&signer.hCryptProv, cspNameW, NULL,
+         PROV_RSA_FULL, 0);
+    ok(ret, "CryptAcquireContextW failed: %x\n", GetLastError());
+    msg = CryptMsgOpenToEncode(PKCS_7_ASN_ENCODING,
+     CMSG_DETACHED_FLAG, CMSG_SIGNED, &signInfo, NULL, NULL);
+    ok(msg != NULL, "CryptMsgOpenToEncode failed: %x\n", GetLastError());
+    /* CMSG_SIGNED allows non-final updates. */
+    ret = CryptMsgUpdate(msg, msgData, sizeof(msgData), FALSE);
+    todo_wine
+    ok(ret, "CryptMsgUpdate failed: %x\n", GetLastError());
+    /* CMSG_SIGNED also allows non-final updates with no data. */
+    ret = CryptMsgUpdate(msg, NULL, 0, FALSE);
+    todo_wine
+    ok(ret, "CryptMsgUpdate failed: %x\n", GetLastError());
+    /* The final update requires a private key in the hCryptProv, in order to
+     * generate the signature.
+     */
+    SetLastError(0xdeadbeef);
+    ret = CryptMsgUpdate(msg, NULL, 0, TRUE);
+    todo_wine
+    ok(!ret && GetLastError() == NTE_BAD_KEYSET,
+     "Expected NTE_BAD_KEYSET, got %x\n", GetLastError());
+    ret = CryptImportKey(signer.hCryptProv, (LPBYTE)privKey, sizeof(privKey),
+     0, 0, &key);
+    ok(ret, "CryptImportKey failed: %08x\n", GetLastError());
+    /* The final update should be able to succeed now that a key exists, but
+     * the previous (invalid) final update prevents it.
+     */
+    SetLastError(0xdeadbeef);
+    ret = CryptMsgUpdate(msg, NULL, 0, TRUE);
+    ok(!ret && GetLastError() == CRYPT_E_MSG_ERROR,
+     "Expected CRYPT_E_MSG_ERROR, got %x\n", GetLastError());
+    CryptMsgClose(msg);
+
+    msg = CryptMsgOpenToEncode(PKCS_7_ASN_ENCODING,
+     CMSG_DETACHED_FLAG, CMSG_SIGNED, &signInfo, NULL, NULL);
+    ok(msg != NULL, "CryptMsgOpenToEncode failed: %x\n", GetLastError());
+    /* CMSG_SIGNED allows non-final updates. */
+    ret = CryptMsgUpdate(msg, msgData, sizeof(msgData), FALSE);
+    todo_wine
+    ok(ret, "CryptMsgUpdate failed: %x\n", GetLastError());
+    /* CMSG_SIGNED also allows non-final updates with no data. */
+    ret = CryptMsgUpdate(msg, NULL, 0, FALSE);
+    todo_wine
+    ok(ret, "CryptMsgUpdate failed: %x\n", GetLastError());
+    /* Now that the private key exists, the final update can succeed (even
+     * with no data.)
+     */
+    ret = CryptMsgUpdate(msg, NULL, 0, TRUE);
+    todo_wine
+    ok(ret, "CryptMsgUpdate failed: %x\n", GetLastError());
+    /* But no updates are allowed after the final update. */
+    SetLastError(0xdeadbeef);
+    ret = CryptMsgUpdate(msg, NULL, 0, FALSE);
+    ok(!ret && GetLastError() == CRYPT_E_MSG_ERROR,
+     "Expected CRYPT_E_MSG_ERROR, got %x\n", GetLastError());
+    SetLastError(0xdeadbeef);
+    ret = CryptMsgUpdate(msg, NULL, 0, TRUE);
+    ok(!ret && GetLastError() == CRYPT_E_MSG_ERROR,
+     "Expected CRYPT_E_MSG_ERROR, got %x\n", GetLastError());
+    CryptMsgClose(msg);
+
+    CryptDestroyKey(key);
+    CryptReleaseContext(signer.hCryptProv, 0);
+    CryptAcquireContextW(&signer.hCryptProv, cspNameW, NULL, PROV_RSA_FULL,
+     CRYPT_DELETEKEYSET);
+}
+
 static void test_signed_msg(void)
 {
     test_signed_msg_open();
+    test_signed_msg_update();
 }
 
 static CRYPT_DATA_BLOB b4 = { 0, NULL };