diff --git a/mats/4.ms b/mats/4.ms
index c302bcb23e..a1f983e722 100644
--- a/mats/4.ms
+++ b/mats/4.ms
@@ -316,7 +316,7 @@
   (equivalent-expansion? 
      (parameterize ([optimize-level 2] [enable-cp0 #t] [#%$suppress-primitive-inlining #f])
        (expand/optimize '(if (begin (set! x y) (if (begin (set! z y) (zero? h)) #t #f)) e1 e2)))
-     '(begin (set! x y) (if (begin (set! z y) (#2%zero? h)) e1 e2)))
+     '(if (begin (set! x y) (set! z y) (#2%zero? h)) e1 e2))
 
   (equivalent-expansion? 
      (parameterize ([optimize-level 2] [enable-cp0 #t] [#%$suppress-primitive-inlining #f])
diff --git a/s/cp0.ss b/s/cp0.ss
index c537959f80..d5eeefefc7 100644
--- a/s/cp0.ss
+++ b/s/cp0.ss
@@ -794,6 +794,10 @@
                 (record-equal? e1 e2 (if (eq? ctxt 'test) 'test 'value))
                 (simple? e1))
            e1]
+          [(and (cp0-constant? (lambda (x) (eq? x #f)) e3)
+                (cp0-constant? (lambda (x) (eq? x #t)) e2)
+                (or (boolean-valued? e1) (eq? ctxt 'test)))
+           (make-nontail ctxt e1)]
           [(nanopass-case (Lsrc Expr) (result-exp e1)
              [(if ,e11 ,[result-exp : e12 -> re12] ,[result-exp : e13 -> re13])
               (if (and (cp0-constant? re12) (cp0-constant? re13))