diff --git a/library/ssl_misc.h b/library/ssl_misc.h
index b7f1440bb8..dad1c82a12 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -1929,7 +1929,7 @@ static inline int mbedtls_ssl_tls13_some_psk_enabled( mbedtls_ssl_context *ssl )
  * Helper functions for extensions checking and convert.
  */
 
-uint32_t mbedtls_tls13_get_extension_mask( uint16_t extension_type );
+uint32_t mbedtls_tls13_get_extension_mask( unsigned int extension_type );
 
 MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_tls13_check_received_extensions( mbedtls_ssl_context *ssl,
diff --git a/library/ssl_tls13_generic.c b/library/ssl_tls13_generic.c
index 7b66be1c73..2fbcdf063c 100644
--- a/library/ssl_tls13_generic.c
+++ b/library/ssl_tls13_generic.c
@@ -1528,7 +1528,7 @@ int mbedtls_ssl_tls13_generate_and_write_ecdh_key_exchange(
 }
 #endif /* MBEDTLS_ECDH_C */
 
-uint32_t mbedtls_tls13_get_extension_mask( uint16_t extension_type )
+uint32_t mbedtls_tls13_get_extension_mask( unsigned int extension_type )
 {
     switch( extension_type )
     {