diff --git a/lib/datalog/scoreboard.json b/lib/datalog/scoreboard.json
index 43ef5417..b1366855 100644
--- a/lib/datalog/scoreboard.json
+++ b/lib/datalog/scoreboard.json
@@ -1,8 +1,8 @@
 {
   "lang": "datalog",
-  "total_passed": 220,
+  "total_passed": 221,
   "total_failed": 0,
-  "total": 220,
+  "total": 221,
   "suites": [
     {"name":"tokenize","passed":26,"failed":0,"total":26},
     {"name":"parse","passed":18,"failed":0,"total":18},
@@ -13,8 +13,8 @@
     {"name":"negation","passed":10,"failed":0,"total":10},
     {"name":"aggregates","passed":19,"failed":0,"total":19},
     {"name":"api","passed":20,"failed":0,"total":20},
-    {"name":"magic","passed":22,"failed":0,"total":22},
+    {"name":"magic","passed":23,"failed":0,"total":23},
     {"name":"demo","passed":21,"failed":0,"total":21}
   ],
-  "generated": "2026-05-08T10:27:32+00:00"
+  "generated": "2026-05-08T10:29:04+00:00"
 }
diff --git a/lib/datalog/scoreboard.md b/lib/datalog/scoreboard.md
index 65bbd501..dda4e89d 100644
--- a/lib/datalog/scoreboard.md
+++ b/lib/datalog/scoreboard.md
@@ -1,6 +1,6 @@
 # datalog scoreboard
 
-**220 / 220 passing** (0 failure(s)).
+**221 / 221 passing** (0 failure(s)).
 
 | Suite | Passed | Total | Status |
 |-------|--------|-------|--------|
@@ -13,5 +13,5 @@
 | negation | 10 | 10 | ok |
 | aggregates | 19 | 19 | ok |
 | api | 20 | 20 | ok |
-| magic | 22 | 22 | ok |
+| magic | 23 | 23 | ok |
 | demo | 21 | 21 | ok |
diff --git a/lib/datalog/tests/magic.sx b/lib/datalog/tests/magic.sx
index 6527aa42..d5a6ca0f 100644
--- a/lib/datalog/tests/magic.sx
+++ b/lib/datalog/tests/magic.sx
@@ -256,6 +256,18 @@
                 (and (= semi-count 78) (= magic-count 12))))))
         true)
 
+      ;; Magic + arithmetic: rules with `is` clauses pass through
+      ;; the rewriter unchanged (built-ins aren't propagated).
+      (dl-mt-test! "magic preserves arithmetic"
+        (let
+          ((source "n(1). n(2). n(3).
+                    doubled(X, Y) :- n(X), is(Y, *(X, 2))."))
+          (let
+            ((semi (dl-eval source "?- doubled(2, Y)."))
+              (magic (dl-eval-magic source "?- doubled(2, Y).")))
+            (= (len semi) (len magic))))
+        true)
+
       (dl-mt-test! "magic skips irrelevant clusters"
         (let
           ;; Two disjoint chains. Query is rooted in cluster 1.