diff --git a/library/bignum.c b/library/bignum.c
index 89fbe12..73ea453 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -893,7 +893,12 @@
 
     if( X == B )
     {
-        const mpi *T = A; A = X; B = T;
+        const mpi *T;
+
+        if( B == A)
+            return mpi_shift_l( X, 1 );
+
+        T = A; A = X; B = T;
     }
 
     if( X != A )