diff --git a/programs/pkey/dh_genprime.c b/programs/pkey/dh_genprime.c
index dbe9153..360e355 100644
--- a/programs/pkey/dh_genprime.c
+++ b/programs/pkey/dh_genprime.c
@@ -156,7 +156,7 @@
         goto exit;
     }
 
-    if( ( ret = mbedtls_mpi_is_prime( &Q, mbedtls_ctr_drbg_random, &ctr_drbg ) ) != 0 )
+    if( ( ret = mbedtls_mpi_is_prime_ext( &Q, 50, mbedtls_ctr_drbg_random, &ctr_drbg ) ) != 0 )
     {
         mbedtls_printf( " failed\n  ! mbedtls_mpi_is_prime returned %d\n\n", ret );
         goto exit;