diff --git a/library/bignum.c b/library/bignum.c
index 12c72af..f479bc9 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -356,6 +356,9 @@
 {
     size_t i, j;
 
+    if( X->n == 0 )
+        return( 0 );
+
     for( i = X->n - 1; i > 0; i-- )
         if( X->p[i] != 0 )
             break;