diff --git a/library/ecp_invasive.h b/library/ecp_invasive.h
index 68187ac..4cf4f6e 100644
--- a/library/ecp_invasive.h
+++ b/library/ecp_invasive.h
@@ -196,7 +196,7 @@
 #if defined(MBEDTLS_ECP_DP_CURVE448_ENABLED)
 
 MBEDTLS_STATIC_TESTABLE
-int mbedtls_ecp_mod_p448(mbedtls_mpi *N);
+int mbedtls_ecp_mod_p448(mbedtls_mpi_uint *N, size_t N_limbs);
 
 #endif /* MBEDTLS_ECP_DP_CURVE448_ENABLED */