diff --git a/lib/hyperscript/compiler.sx b/lib/hyperscript/compiler.sx
index f1784c70..86f80029 100644
--- a/lib/hyperscript/compiler.sx
+++ b/lib/hyperscript/compiler.sx
@@ -364,10 +364,7 @@
           (true
             (let
               ((t (hs-to-sx expr)))
-              (list
-                (quote set!)
-                t
-                (list (quote +) (list (quote or) t 0) amount)))))))
+              (list (quote set!) t (list (quote +) t amount)))))))
     (define
       emit-dec
       (fn
@@ -416,10 +413,7 @@
           (true
             (let
               ((t (hs-to-sx expr)))
-              (list
-                (quote set!)
-                t
-                (list (quote -) (list (quote or) t 0) amount)))))))
+              (list (quote set!) t (list (quote -) t amount)))))))
     (define
       emit-behavior
       (fn
diff --git a/lib/hyperscript/integration.sx b/lib/hyperscript/integration.sx
index 8e17242c..7fd9bf4b 100644
--- a/lib/hyperscript/integration.sx
+++ b/lib/hyperscript/integration.sx
@@ -10,20 +10,46 @@
 ;; Returns a function (fn (me) ...) that can be called with a DOM element.
 ;; Uses eval-expr-cek to turn the SX data structure into a live closure.
 
-(define
-  hs-handler
-  (fn
-    (src)
-    (let
-      ((sx (hs-to-sx-from-source src)))
-      (eval-expr-cek
-        (list
-          (quote fn)
-          (list (quote me))
-          (list
-            (quote let)
-            (list (list (quote it) nil) (list (quote event) nil))
-            sx))))))
+(begin
+  (define
+    hs-collect-vars
+    (fn
+      (sx)
+      (define vars (list))
+      (define
+        walk
+        (fn
+          (node)
+          (when
+            (list? node)
+            (when
+              (and
+                (> (len node) 1)
+                (= (first node) (quote set!))
+                (symbol? (nth node 1)))
+              (let
+                ((name (nth node 1)))
+                (when
+                  (not (some (fn (v) (= v name)) vars))
+                  (set! vars (cons name vars)))))
+            (for-each walk node))))
+      (walk sx)
+      vars))
+  (define
+    hs-handler
+    (fn
+      (src)
+      (let
+        ((sx (hs-to-sx-from-source src)))
+        (let
+          ((extra-vars (hs-collect-vars sx)))
+          (let
+            ((bindings (append (list (list (quote it) nil) (list (quote event) nil)) (map (fn (v) (list v nil)) extra-vars))))
+            (eval-expr-cek
+              (list
+                (quote fn)
+                (list (quote me))
+                (list (quote let) bindings sx)))))))))
 
 ;; ── Activate a single element ───────────────────────────────────
 ;; Reads the _="..." attribute, compiles, and executes with me=element.