diff --git a/library/bignum_mod.c b/library/bignum_mod.c
index 7c89b57d7f..31e18e7410 100644
--- a/library/bignum_mod.c
+++ b/library/bignum_mod.c
@@ -276,7 +276,7 @@ int mbedtls_mpi_mod_inv( mbedtls_mpi_mod_residue *X,
 
     mbedtls_platform_zeroize( working_memory,
                               working_limbs * sizeof(mbedtls_mpi_uint) );
-    free( working_memory );
+    mbedtls_free( working_memory );
 
     return ret;
 }