diff --git a/library/rsa.c b/library/rsa.c
index 0a6c490..a0f750e 100644
--- a/library/rsa.c
+++ b/library/rsa.c
@@ -253,7 +253,7 @@
         return( POLARSSL_ERR_RSA_BAD_INPUT_DATA );
     }
 
-#if 0
+#if defined(POLARSSL_RSA_NO_CRT)
     MPI_CHK( mpi_exp_mod( &T, &T, &ctx->D, &ctx->N, &ctx->RN ) );
 #else
     /*