diff --git a/src/libmp/port/mptouv.c b/src/libmp/port/mptouv.c
index aa5af05b..eb663f38 100644
--- a/src/libmp/port/mptouv.c
+++ b/src/libmp/port/mptouv.c
@@ -46,7 +46,7 @@ mptouv(mpint *b)
 
 	v = 0ULL;
 	for(s = 0; s < b->top; s++)
-		v |= b->p[s]<<(s*sizeof(mpdigit)*8);
+		v |= (uvlong)b->p[s]<<(s*sizeof(mpdigit)*8);
 
 	return v;
 }