diff --git a/library/bignum.c b/library/bignum.c
index 317c7cc..4b8edd7 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -942,7 +942,7 @@
     ret |= y & cond;
 
 
-    ret = ret >> ( sizeof( mbedtls_mpi_uint ) * 8 - 1 );
+    ret = ret >> ( biL - 1 );
 
     return ret;
 }