diff --git a/library/ecp_internal.h b/library/ecp_internal.h
new file mode 100644
index 0000000..07bf386
--- /dev/null
+++ b/library/ecp_internal.h
@@ -0,0 +1,34 @@
+/**
+ * \file ecp_internal.h
+ *
+ * \brief Function declarations for internal functions of elliptic curve
+ * point arithmetic.
+ */
+/**
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+#ifndef MBEDTLS_ECP_INTERNAL_H
+#define MBEDTLS_ECP_INTERNAL_H
+
+#include "common.h"
+#include "mbedtls/bignum.h"
+#include "bignum_mod.h"
+
+int mbedtls_ecp_quasi_reduction(mbedtls_mpi_uint *X,
+                                const mbedtls_mpi_mod_modulus *N);
+
+#endif /* MBEDTLS_ECP_INTERNAL_H */