diff --git a/library/rsa.c b/library/rsa.c
index 4ee9308..8623011 100644
--- a/library/rsa.c
+++ b/library/rsa.c
@@ -923,7 +923,7 @@
 
 size_t mbedtls_rsa_get_len( const mbedtls_rsa_context *ctx )
 {
-    return( mbedtls_mpi_size( &ctx->N ) );
+    return( ctx->len );
 }