diff --git a/libbf.c b/libbf.c
index fe1628e79..63e7daeb3 100644
--- a/libbf.c
+++ b/libbf.c
@@ -235,8 +235,13 @@ int bf_set_ui(bf_t *r, uint64_t a)
         a0 = a;
         a1 = a >> 32;
         shift = clz(a1);
+        // shift < 32 because a > 0xffffffff
         r->tab[0] = a0 << shift;
-        r->tab[1] = (a1 << shift) | (a0 >> (LIMB_BITS - shift));
+        if (shift == 0) {
+            r->tab[1] = a1;
+        } else {
+            r->tab[1] = (a1 << shift) | (a0 >> (LIMB_BITS - shift));
+        }
         r->expn = 2 * LIMB_BITS - shift;
     }
 #endif