diff --git a/library/ecp_curves.c b/library/ecp_curves.c
index 16800aa..1808152 100644
--- a/library/ecp_curves.c
+++ b/library/ecp_curves.c
@@ -5431,6 +5431,13 @@
 MBEDTLS_STATIC_TESTABLE
 int mbedtls_ecp_mod_p255_raw(mbedtls_mpi_uint *X, size_t X_Limbs)
 {
+
+    if (X_Limbs > 2*P255_WIDTH) {
+        X_Limbs = 2*P255_WIDTH;
+    } else if (X_Limbs < P255_WIDTH) {
+        return 0;
+    }
+
     mbedtls_mpi_uint *carry = mbedtls_calloc(P255_WIDTH, ciL);
     if (carry == NULL) {
         return MBEDTLS_ERR_ECP_ALLOC_FAILED;