diff --git a/src/x509.c b/src/x509.c
index d85d8db968..8da2ffdf57 100644
--- a/src/x509.c
+++ b/src/x509.c
@@ -7526,11 +7526,24 @@ int wolfSSL_i2d_X509(WOLFSSL_X509* x509, unsigned char** out)
 int wc_GeneratePreTBS(DecodedCert* cert, byte *der, int derSz) {
     int ret = 0;
     WOLFSSL_X509 *x = NULL;
+    byte certOwnsAltNames = 0;
+    byte certIsCSR = 0;
 
     if ((cert == NULL) || (der == NULL) || (derSz <= 0)) {
         return BAD_FUNC_ARG;
     }
 
+    /* The call to CopyDecodedToX509() transfers ownership of the altNames in
+     * the DecodedCert to the temporary X509 object, causing the list to be
+     * freed in wolfSSL_X509_free(). As this is an unintended side-effect, we
+     * have to save the ownerFlag here and transfer ownership back to the
+     * DecodedCert prior to freeing the X509 object. */
+    certOwnsAltNames = cert->weOwnAltNames;
+
+#ifdef WOLFSSL_CERT_REQ
+    certIsCSR = cert->isCSR;
+#endif
+
     x = wolfSSL_X509_new();
     if (x == NULL) {
         ret = MEMORY_E;
@@ -7539,6 +7552,9 @@ int wc_GeneratePreTBS(DecodedCert* cert, byte *der, int derSz) {
         ret = CopyDecodedToX509(x, cert);
     }
 
+    /* CopyDecodedToX509() clears cert->weOwnAltNames. Restore it. */
+    cert->weOwnAltNames = certOwnsAltNames;
+
     if (ret == 0) {
         /* Remove the altsigval extension. */
         XFREE(x->altSigValDer, x->heap, DYNAMIC_TYPE_X509_EXT);
@@ -7547,13 +7563,16 @@ int wc_GeneratePreTBS(DecodedCert* cert, byte *der, int derSz) {
         /* Remove sigOID so it won't be encoded. */
         x->sigOID = 0;
         /* We now have a PreTBS. Encode it. */
-        ret = wolfssl_x509_make_der(x, 0, der, &derSz, 0);
+        ret = wolfssl_x509_make_der(x, certIsCSR, der, &derSz, 0);
         if (ret == WOLFSSL_SUCCESS) {
             ret = derSz;
         }
     }
 
     if (x != NULL) {
+        /* Safe the altNames list from being freed unitentionally. */
+        x->altNames = NULL;
+
         wolfSSL_X509_free(x);
     }
 
diff --git a/wolfcrypt/src/asn.c b/wolfcrypt/src/asn.c
index b444af94cb..f5ed8804ff 100644
--- a/wolfcrypt/src/asn.c
+++ b/wolfcrypt/src/asn.c
@@ -23864,13 +23864,12 @@ int ParseCertRelative(DecodedCert* cert, int type, int verify, void* cm)
                 #ifndef WOLFSSL_SMALL_STACK
                     byte der[MAX_CERT_VERIFY_SZ];
                 #else
-                    byte *der = (byte*)XMALLOC(MAX_CERT_VERIFY_SZ, ssl->heap,
+                    byte *der = (byte*)XMALLOC(MAX_CERT_VERIFY_SZ, cert->heap,
                                             DYNAMIC_TYPE_DCERT);
                     if (der == NULL) {
                         ret = MEMORY_E;
                     } else
                 #endif /* ! WOLFSSL_SMALL_STACK */
-
                     {
                         ret = wc_GeneratePreTBS(cert, der, MAX_CERT_VERIFY_SZ);
 
@@ -23882,7 +23881,7 @@ int ParseCertRelative(DecodedCert* cert, int type, int verify, void* cm)
                                     NULL, 0, NULL);
                         }
                 #ifdef WOLFSSL_SMALL_STACK
-                        XFREE(der, ssl->heap, DYNAMIC_TYPE_DCERT);
+                        XFREE(der, cert->heap, DYNAMIC_TYPE_DCERT);
                 #endif /* WOLFSSL_SMALL_STACK */
 
                         if (ret != 0) {
@@ -23912,6 +23911,7 @@ int ParseCertRelative(DecodedCert* cert, int type, int verify, void* cm)
         }
 #ifdef WOLFSSL_CERT_REQ
         else if (type == CERTREQ_TYPE) {
+            /* try to confirm/verify signature */
             if ((ret = ConfirmSignature(&cert->sigCtx,
                     cert->source + cert->certBegin,
                     cert->sigIndex - cert->certBegin,
@@ -23930,6 +23930,44 @@ int ParseCertRelative(DecodedCert* cert, int type, int verify, void* cm)
                 WOLFSSL_ERROR_VERBOSE(ret);
                 return ret;
             }
+
+        #ifdef WOLFSSL_DUAL_ALG_CERTS
+            if ((ret == 0) && cert->extAltSigAlgSet &&
+                cert->extAltSigValSet) {
+            #ifndef WOLFSSL_SMALL_STACK
+                byte der[MAX_CERT_VERIFY_SZ];
+            #else
+                byte *der = (byte*)XMALLOC(MAX_CERT_VERIFY_SZ, cert->heap,
+                                        DYNAMIC_TYPE_DCERT);
+                if (der == NULL) {
+                    ret = MEMORY_E;
+                } else
+            #endif /* ! WOLFSSL_SMALL_STACK */
+                {
+                    ret = wc_GeneratePreTBS(cert, der, MAX_CERT_VERIFY_SZ);
+
+                    if (ret > 0) {
+                        ret = ConfirmSignature(&cert->sigCtx, der, ret,
+                                cert->sapkiDer, cert->sapkiLen,
+                                cert->sapkiOID, cert->altSigValDer,
+                                cert->altSigValLen, cert->altSigAlgOID,
+                                NULL, 0, NULL);
+                    }
+            #ifdef WOLFSSL_SMALL_STACK
+                    XFREE(der, cert->heap, DYNAMIC_TYPE_DCERT);
+            #endif /* WOLFSSL_SMALL_STACK */
+
+                    if (ret != 0) {
+                        WOLFSSL_MSG("Confirm alternative signature failed");
+                        WOLFSSL_ERROR_VERBOSE(ret);
+                        return ret;
+                    }
+                    else {
+                        WOLFSSL_MSG("Alt signature has been verified!");
+                    }
+                }
+            }
+        #endif /* WOLFSSL_DUAL_ALG_CERTS */
         }
 #endif
         else {