diff --git a/library/ssl_tls13_keys.c b/library/ssl_tls13_keys.c
index 895176d..ff4aa0e 100644
--- a/library/ssl_tls13_keys.c
+++ b/library/ssl_tls13_keys.c
@@ -64,7 +64,7 @@
  *                   hardcoding the writing of the high bytes.
  * - (label, label_len): label + label length, without "tls13 " prefix
  *                       The label length MUST be less than or equal to
- *                       MBEDTLS_SSL_TLS1_3_KEY_SCHEDULE_MAX_LABEL_LEN
+ *                       MBEDTLS_SSL_TLS1_3_HKDF_LABEL_MAX_LABEL_LEN.
  *                       It is the caller's responsibility to ensure this.
  *                       All (label, label length) pairs used in TLS 1.3
  *                       can be obtained via MBEDTLS_SSL_TLS1_3_LBL_WITH_LEN().
@@ -91,7 +91,7 @@
 #define SSL_TLS1_3_KEY_SCHEDULE_MAX_HKDF_LABEL_LEN                      \
     SSL_TLS1_3_KEY_SCHEDULE_HKDF_LABEL_LEN(                             \
         sizeof(tls13_label_prefix) +                       \
-        MBEDTLS_SSL_TLS1_3_KEY_SCHEDULE_MAX_LABEL_LEN,     \
+        MBEDTLS_SSL_TLS1_3_HKDF_LABEL_MAX_LABEL_LEN,       \
         MBEDTLS_SSL_TLS1_3_KEY_SCHEDULE_MAX_CONTEXT_LEN)
 
 static void ssl_tls13_hkdf_encode_label(
@@ -147,7 +147,7 @@
     psa_key_derivation_operation_t operation =
         PSA_KEY_DERIVATION_OPERATION_INIT;
 
-    if (label_len > MBEDTLS_SSL_TLS1_3_KEY_SCHEDULE_MAX_LABEL_LEN) {
+    if (label_len > MBEDTLS_SSL_TLS1_3_HKDF_LABEL_MAX_LABEL_LEN) {
         /* Should never happen since this is an internal
          * function, and we know statically which labels
          * are allowed. */
diff --git a/library/ssl_tls13_keys.h b/library/ssl_tls13_keys.h
index 31ffe44..14f6e48 100644
--- a/library/ssl_tls13_keys.h
+++ b/library/ssl_tls13_keys.h
@@ -60,8 +60,9 @@
     mbedtls_ssl_tls13_labels.LABEL,              \
     MBEDTLS_SSL_TLS1_3_LBL_LEN(LABEL)
 
-#define MBEDTLS_SSL_TLS1_3_KEY_SCHEDULE_MAX_LABEL_LEN  \
-    sizeof(union mbedtls_ssl_tls13_labels_union)
+/* Maximum length of the label field in the HkdfLabel struct defined in
+ * RFC 8446, Section 7.1, excluding the "tls13 " prefix. */
+#define MBEDTLS_SSL_TLS1_3_HKDF_LABEL_MAX_LABEL_LEN 249
 
 /* The maximum length of HKDF contexts used in the TLS 1.3 standard.
  * Since contexts are always hashes of message transcripts, this can