diff --git a/scripts/generate_psa_constants.py b/scripts/generate_psa_constants.py
index 3e4e88b..bcda282 100755
--- a/scripts/generate_psa_constants.py
+++ b/scripts/generate_psa_constants.py
@@ -62,7 +62,10 @@
         }
     } else if (PSA_ALG_IS_AEAD(alg)) {
         core_alg = PSA_ALG_AEAD_WITH_DEFAULT_TAG_LENGTH(alg);
-        if (core_alg != alg) {
+        if (core_alg == 0) {
+            /* For unkonwn AEAD algorithms, there is no "default tag length". */
+            core_alg = alg;
+        } else if (core_alg != alg) {
             append(&buffer, buffer_size, &required_size,
                    "PSA_ALG_AEAD_WITH_TAG_LENGTH(", 29);
             length_modifier = PSA_AEAD_TAG_LENGTH(alg);
@@ -73,7 +76,7 @@
     default:
         %(algorithm_code)s{
             append_integer(&buffer, buffer_size, &required_size,
-                           "0x%%08lx", (unsigned long) alg);
+                           "0x%%08lx", (unsigned long) core_alg);
         }
         break;
     }