diff --git a/library/bignum.c b/library/bignum.c
index 5dca3a9..67add49 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -2328,7 +2328,7 @@
     /*
      * Load the result in the output variable.
      */
-    mbedtls_mpi_copy(X, &W[x_index]);
+    MBEDTLS_MPI_CHK(mbedtls_mpi_copy(X, &W[x_index]));
 
 cleanup: