diff --git a/mud.c b/mud.c
index 23bd12e..1387c4e 100644
--- a/mud.c
+++ b/mud.c
@@ -1144,8 +1144,8 @@ mud_stat_update(struct mud_stat *stat, const uint64_t val)
 {
     if (stat->setup) {
         const uint64_t var = mud_abs_diff(stat->val, val);
-        stat->var = ((stat->var << 1) + stat->var + var) >> 2;
-        stat->val = ((stat->val << 3) - stat->val + val) >> 3;
+        stat->var = ((var << 1) + var + stat->var) >> 2;
+        stat->val = ((val << 3) - val + stat->val) >> 3;
     } else {
         stat->setup = 1;
         stat->var = val >> 1;