diff --git a/library/ecp_curves.c b/library/ecp_curves.c
index 9e70e8e..571b0fe 100644
--- a/library/ecp_curves.c
+++ b/library/ecp_curves.c
@@ -5223,7 +5223,7 @@
     /* Helper references for top part of N */
     mbedtls_mpi_uint * const NT_p = N->p + P255_WIDTH;
     const size_t NT_n = N->n - P255_WIDTH;
-    if( NT_n <= P255_WIDTH )
+    if( N->n <= P255_WIDTH )
         return( 0 );
 
     /* Split N as N + 2^256 M */