diff --git a/library/ssl_tls13_generic.c b/library/ssl_tls13_generic.c
index 7b66be1..2fbcdf0 100644
--- a/library/ssl_tls13_generic.c
+++ b/library/ssl_tls13_generic.c
@@ -1528,7 +1528,7 @@
 }
 #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 )
     {