diff --git a/library/ecp_invasive.h b/library/ecp_invasive.h
index b7cd6e2..bd6d399 100644
--- a/library/ecp_invasive.h
+++ b/library/ecp_invasive.h
@@ -186,6 +186,13 @@
 
 #endif /* MBEDTLS_ECP_DP_SECP224K1_ENABLED */
 
+#if defined(MBEDTLS_ECP_DP_SECP256K1_ENABLED)
+
+MBEDTLS_STATIC_TESTABLE
+int ecp_mod_p256k1(mbedtls_mpi *N);
+
+#endif /* MBEDTLS_ECP_DP_SECP256K1_ENABLED */
+
 /** Initialise a modulus with hard-coded const curve data.
  *
  * \note            The caller is responsible for the \p N modulus' memory.