diff --git a/collects/compiler/decompile.ss b/collects/compiler/decompile.ss
index be61752ce8..c1d5f9cd77 100644
--- a/collects/compiler/decompile.ss
+++ b/collects/compiler/decompile.ss
@@ -207,9 +207,9 @@
        ,@(map (lambda (lam)
                 (decompile-lam lam globs stack closed))
               lams))]
-    [(struct let-one (rhs body flonum?))
+    [(struct let-one (rhs body flonum? unused?))
      (let ([id (or (extract-id rhs)
-                   (gensym 'local))])
+                   (gensym (if unused? 'unused 'local)))])
        `(let ([,id ,(let ([v (decompile-expr rhs globs (cons id stack) closed)])
                       (if flonum?
                           (list '#%as-flonum v)
diff --git a/collects/compiler/zo-marshal.ss b/collects/compiler/zo-marshal.ss
index 2ac973aba1..a174d35642 100644
--- a/collects/compiler/zo-marshal.ss
+++ b/collects/compiler/zo-marshal.ss
@@ -160,7 +160,7 @@
     [(struct case-lam (name lams))
      (traverse-data name visit)
      (for-each (lambda (lam) (traverse-lam lam visit)) lams)]
-    [(struct let-one (rhs body flonum?))
+    [(struct let-one (rhs body flonum? unused?))
      (traverse-expr rhs visit)
      (traverse-expr body visit)]
     [(struct let-void (count boxes? body))
@@ -297,7 +297,8 @@
   CPT_PATH
   CPT_CLOSURE
   CPT_DELAY_REF
-  CPT_PREFAB)
+  CPT_PREFAB
+  CPT_LET_ONE_UNUSED)
 
 (define-enum
   0
@@ -314,7 +315,7 @@
   APPVALS_EXPD
   SPLICE_EXPD)
 
-(define CPT_SMALL_NUMBER_START 35)
+(define CPT_SMALL_NUMBER_START 36)
 (define CPT_SMALL_NUMBER_END 60)
 
 (define CPT_SMALL_SYMBOL_START 60)
@@ -715,8 +716,12 @@
                     (cons (or name null)
                           lams)
                     out)]
-    [(struct let-one (rhs body flonum?))
-     (out-byte (if flonum? CPT_LET_ONE_FLONUM CPT_LET_ONE) out)
+    [(struct let-one (rhs body flonum? unused?))
+     (out-byte (cond
+                [flonum? CPT_LET_ONE_FLONUM]
+                [unused? CPT_LET_ONE_UNUSED]
+                [else CPT_LET_ONE])
+               out)
      (out-expr (protect-quote rhs) out)
      (out-expr (protect-quote body) out)]
     [(struct let-void (count boxes? body))
diff --git a/collects/compiler/zo-parse.ss b/collects/compiler/zo-parse.ss
index 868d7cbff2..37c3dcd2d6 100644
--- a/collects/compiler/zo-parse.ss
+++ b/collects/compiler/zo-parse.ss
@@ -412,7 +412,8 @@
     [32 closure]
     [33 delayed]
     [34 prefab]
-    [35 60 small-number]
+    [35 let-one-unused]
+    [36 60 small-number]
     [60 80 small-symbol]
     [80 92 small-marshalled]
     [92 ,(+ 92 small-list-max) small-proper-list]
@@ -766,9 +767,10 @@
                            (if ppr null (read-compact cp)))
                      (read-compact-list l ppr cp))
                  (loop l ppr)))]
-          [(let-one let-one-flonum)
+          [(let-one let-one-flonum let-one-unused)
            (make-let-one (read-compact cp) (read-compact cp)
-                         (eq? cpt-tag 'let-one-flonum))]
+                         (eq? cpt-tag 'let-one-flonum)
+                         (eq? cpt-tag 'let-one-unused))]
           [(branch)
            (make-branch (read-compact cp) (read-compact cp) (read-compact cp))]
           [(module-index) (module-path-index-join (read-compact cp) (read-compact cp))]
diff --git a/collects/compiler/zo-structs.ss b/collects/compiler/zo-structs.ss
index cd37ba4a5a..a1f8f982a8 100644
--- a/collects/compiler/zo-structs.ss
+++ b/collects/compiler/zo-structs.ss
@@ -118,7 +118,7 @@
 (define-form-struct (closure expr) ([code lam?] [gen-id symbol?])) ; a static closure (nothing to close over)
 (define-form-struct (case-lam expr) ([name (or/c symbol? vector? empty?)] [clauses (listof (or/c lam? indirect?))])) ; each clause is a lam (added indirect)
 
-(define-form-struct (let-one expr) ([rhs (or/c expr? seq? indirect? any/c)] [body (or/c expr? seq? indirect? any/c)] [flonum? boolean?])) ; pushes one value onto stack
+(define-form-struct (let-one expr) ([rhs (or/c expr? seq? indirect? any/c)] [body (or/c expr? seq? indirect? any/c)] [flonum? boolean?] [unused? boolean?])) ; pushes one value onto stack
 (define-form-struct (let-void expr) ([count exact-nonnegative-integer?] [boxes? boolean?] [body (or/c expr? seq? indirect? any/c)])) ; create new stack slots
 (define-form-struct (install-value expr) ([count exact-nonnegative-integer?] 
                                           [pos exact-nonnegative-integer?]