diff --git a/library/rsa.c b/library/rsa.c
index 56f4345..35ace85 100644
--- a/library/rsa.c
+++ b/library/rsa.c
@@ -437,8 +437,8 @@
     if( mbedtls_mpi_cmp_int( &ctx->N, 0 ) == 0 ||
         mbedtls_mpi_cmp_int( &ctx->D, 0 ) == 0 ||
         mbedtls_mpi_cmp_int( &ctx->E, 0 ) == 0 ||
-        mbedtls_mpi_cmp_int( &ctx->P, 0 ) == 0 ||
-        mbedtls_mpi_cmp_int( &ctx->Q, 0 ) == 0 )
+        ( f_rng != NULL && mbedtls_mpi_cmp_int( &ctx->P, 0 ) == 0 ) ||
+        ( f_rng != NULL && mbedtls_mpi_cmp_int( &ctx->Q, 0 ) == 0 ) )
     {
         return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
     }