diff --git a/library/ecp_curves.c b/library/ecp_curves.c
index f58539d..269f5fc 100644
--- a/library/ecp_curves.c
+++ b/library/ecp_curves.c
@@ -4584,6 +4584,8 @@
 #endif
 #if defined(MBEDTLS_ECP_DP_SECP521R1_ENABLED)
 static int ecp_mod_p521(mbedtls_mpi *);
+MBEDTLS_STATIC_TESTABLE
+int ecp_mod_p521_raw(mbedtls_mpi_uint *N_p, size_t N_n);
 #endif
 
 #define NIST_MODP(P)      grp->modp = ecp_mod_ ## P;
@@ -5207,7 +5209,9 @@
 cleanup:
     return ret;
 }
-static int ecp_mod_p521_raw(mbedtls_mpi_uint *N_p, size_t N_n)
+
+MBEDTLS_STATIC_TESTABLE
+int ecp_mod_p521_raw(mbedtls_mpi_uint *N_p, size_t N_n)
 {
     mbedtls_mpi_uint carry = 0;
 
diff --git a/library/ecp_invasive.h b/library/ecp_invasive.h
index 3ee238e..31646b9 100644
--- a/library/ecp_invasive.h
+++ b/library/ecp_invasive.h
@@ -95,6 +95,13 @@
 
 #endif /* MBEDTLS_ECP_DP_SECP192R1_ENABLED */
 
+#if defined(MBEDTLS_ECP_DP_SECP521R1_ENABLED)
+
+MBEDTLS_STATIC_TESTABLE
+int ecp_mod_p521_raw(mbedtls_mpi_uint *N_p, size_t N_n);
+
+#endif /* MBEDTLS_ECP_DP_SECP521R1_ENABLED */
+
 #endif /* MBEDTLS_TEST_HOOKS && MBEDTLS_ECP_C */
 
 #endif /* MBEDTLS_ECP_INVASIVE_H */