diff --git a/il-structs.rkt b/il-structs.rkt
index 242ed22..d1bbf64 100644
--- a/il-structs.rkt
+++ b/il-structs.rkt
@@ -132,7 +132,9 @@
 
                                  PopControlFrame
                                  
-                                 DebugPrint))
+                                 DebugPrint
+                                 Comment
+                                 ))
 
 
 ;; Debug print statement.
@@ -215,6 +217,8 @@
   #:transparent)
 
 
+(define-struct: Comment ([val : Any])
+  #:transparent)
 
 
 
diff --git a/js-assembler/assemble.rkt b/js-assembler/assemble.rkt
index b15f763..2dd4d5a 100644
--- a/js-assembler/assemble.rkt
+++ b/js-assembler/assemble.rkt
@@ -154,6 +154,8 @@ EOF
              [(PushControlFrame/Prompt? stmt)
               (next)]
              [(PopControlFrame? stmt)
+              (next)]
+             [(Comment? stmt)
               (next)]))]))
 
 
@@ -292,7 +294,10 @@ EOF
                                         (format "[~a]" (assemble-oparg (PushImmediateOntoEnvironment-value stmt)))]
                                        [else
                                         (assemble-oparg (PushImmediateOntoEnvironment-value stmt))])])
-                    val-string))])))
+                    val-string))]
+     [(Comment? stmt)
+      ;; TODO: maybe comments should be emitted as JavaScript comments.
+      ""])))
 
 
 (define-predicate natural? Natural)
diff --git a/js-assembler/collect-jump-targets.rkt b/js-assembler/collect-jump-targets.rkt
index 766ad44..06f3090 100644
--- a/js-assembler/collect-jump-targets.rkt
+++ b/js-assembler/collect-jump-targets.rkt
@@ -60,6 +60,8 @@
    [(PushControlFrame/Prompt? stmt)
     (label->labels (PushControlFrame/Prompt-label stmt))]
    [(PopControlFrame? stmt)
+    empty]
+   [(Comment? stmt)
     empty]))
 
 
diff --git a/optimize-il.rkt b/optimize-il.rkt
index 491a06c..ce7e0f9 100644
--- a/optimize-il.rkt
+++ b/optimize-il.rkt
@@ -102,6 +102,8 @@
      #f]
     
     [(PopControlFrame? stmt)
+     #f]
+    [(Comment? stmt)
      #f]))
 
 
diff --git a/simulator/simulator.rkt b/simulator/simulator.rkt
index abc4399..cbf230f 100644
--- a/simulator/simulator.rkt
+++ b/simulator/simulator.rkt
@@ -124,6 +124,8 @@
                      (step-push-control-frame/prompt! m i)]
                     [(PopControlFrame? i)
                      (step-pop-control-frame! m i)]
+                    [(Comment? i)
+                     'ok]
                     )])
          (increment-pc! m)))