diff --git a/broken-fact.rkt b/broken-fact.rkt
new file mode 100644
index 0000000..d2ca022
--- /dev/null
+++ b/broken-fact.rkt
@@ -0,0 +1,9 @@
+#lang planet dyoo/whalesong
+
+(define (f x)
+  (if (= x 0)
+      "one"
+      (* x (f (sub1 x)))))
+
+(list (f 3)
+      (f 4))
diff --git a/js-assembler/runtime-src/baselib-check.js b/js-assembler/runtime-src/baselib-check.js
index 99b93a5..c867ce1 100644
--- a/js-assembler/runtime-src/baselib-check.js
+++ b/js-assembler/runtime-src/baselib-check.js
@@ -121,10 +121,12 @@
     var testArity = function (MACHINE, callerName, observed, minimum, maximum) {
         if (observed < minimum || observed > maximum) {
             baselib.exceptions.raise(
-                MACHINE, new Error(callerName + ": expected at least " + minimum
-                                   + " arguments "
-                                   + " but received " + observed));
-
+                MACHINE, 
+                baselib.exceptions.ExnFailContractArity.constructor(
+                    callerName + ": expected at least " + minimum
+                        + " arguments "
+                        + " but received " + observed,
+                    MACHINE.captureContinuationMarks()));
         }
     };
 
diff --git a/js-assembler/runtime-src/baselib-exceptions.js b/js-assembler/runtime-src/baselib-exceptions.js
index 7b88615..ea22c6d 100644
--- a/js-assembler/runtime-src/baselib-exceptions.js
+++ b/js-assembler/runtime-src/baselib-exceptions.js
@@ -65,6 +65,8 @@
     var raise = function(MACHINE, e) { 
         if (isRacketError(e) && Exn.predicate(e.racketError)) {
             e.message = Exn.accessor(e.racketError, 0);
+        } else if (Exn.predicate(e)) {
+            e = new RacketError(Exn.accessor(e, 0), e);
         }
 
         if (typeof(window.console) !== 'undefined' &&
@@ -83,11 +85,9 @@
         var message = baselib.format.format("Not bound: ~a", [name]);
         var contMarks = MACHINE.captureContinuationMarks();
         raise(MACHINE, 
-              new RacketError(
-                  message,
-                  ExnFailContractVariable.constructor(message, 
-                                                      contMarks, 
-                                                      baselib.symbols.makeSymbol(name)))); 
+              ExnFailContractVariable.constructor(message, 
+                                                  contMarks, 
+                                                  baselib.symbols.makeSymbol(name))); 
     };
 
 
@@ -105,16 +105,14 @@
                            expectedTypeName,
                            (argumentOffset + 1),
                            actualValue]);
-            raise(MACHINE, new RacketError(message,
-                                           ExnFailContract.constructor(message, contMarks)));
+            raise(MACHINE, ExnFailContract.constructor(message, contMarks));
         } else {
             message = baselib.format.format(
                           "~a: expected ~a but received ~e",
                           [callerName,
                            expectedTypeName,
                            actualValue]);
-            raise(MACHINE, new RacketError(message,
-                                           ExnFailContract.constructor(message, contMarks)));
+            raise(MACHINE, ExnFailContract.constructor(message, contMarks));
         }
     };
 
@@ -122,9 +120,7 @@
         var message = baselib.format.format("expected ~e values, received ~e values",
                                             [expected, MACHINE.argcount]);
         var contMarks = MACHINE.captureContinuationMarks();
-        raise(MACHINE, 
-              new RacketError(message,
-                              ExnFailContract.constructor(message, contMarks)));
+        raise(MACHINE, ExnFailContract.constructor(message, contMarks));
     };
 
     var raiseArityMismatchError = function(MACHINE, proc, expected, received) {
@@ -133,8 +129,7 @@
                                              expected,
                                              received]);
         raise(MACHINE, 
-              new RacketError(message,
-                              ExnFailContractArity.constructor(message, contMarks)));
+              ExnFailContractArity.constructor(message, contMarks));
     };
 
     var raiseOperatorApplicationError = function(MACHINE, operator) {
@@ -142,8 +137,7 @@
                                             [operator]);
         var contMarks = MACHINE.captureContinuationMarks();
         raise(MACHINE, 
-              new RacketError(message,
-                              ExnFailContract.constructor(message, contMarks)));
+              ExnFailContract.constructor(message, contMarks));
     };
 
     var raiseOperatorIsNotClosure = function(MACHINE, operator) {
@@ -151,8 +145,7 @@
                                             [operator]);
         var contMarks = MACHINE.captureContinuationMarks();
         raise(MACHINE,
-              new RacketError(message,
-                              ExnFailContract.constructor(message, contMarks)));
+              ExnFailContract.constructor(message, contMarks));
     };
 
     var raiseOperatorIsNotPrimitiveProcedure = function(MACHINE, operator) {
@@ -160,16 +153,15 @@
                                             [operator]);
         var contMarks = MACHINE.captureContinuationMarks();
         raise(MACHINE,
-              new RacketError(message,
-                              ExnFailContract.constructor(message, contMarks)));
+              ExnFailContract.constructor(message, contMarks));
     };
 
 
     var raiseUnimplementedPrimitiveError = function(MACHINE, name) {
         var message = "unimplemented kernel procedure: " + name;
         var contMarks = MACHINE.captureContinuationMarks();
-        raise(MACHINE, new RacketError(message,
-                                       ExnFailContract.constructor(message, contMarks)));
+        raise(MACHINE,
+              ExnFailContract.constructor(message, contMarks));
     };
 
 
diff --git a/js-assembler/runtime-src/baselib-functions.js b/js-assembler/runtime-src/baselib-functions.js
index 5b8dac9..e146006 100644
--- a/js-assembler/runtime-src/baselib-functions.js
+++ b/js-assembler/runtime-src/baselib-functions.js
@@ -212,10 +212,11 @@
             return coerseClosureToJavaScript(v, MACHINE);
         } else {
             baselib.exceptions.raise(MACHINE,
-                                         baselib.exceptions.makeExnFail(
-                                             baselib.format.format(
-                                                 "Not a procedure: ~e",
-                                                 v)));
+                                     baselib.exceptions.makeExnFailContract(
+                                         baselib.format.format(
+                                             "Not a procedure: ~e",
+                                             v),
+                                         MACHINE.captureContinuationMarks()));
         }
     };
 
diff --git a/js-assembler/runtime-src/baselib-primitives.js b/js-assembler/runtime-src/baselib-primitives.js
index 036649d..8251351 100644
--- a/js-assembler/runtime-src/baselib-primitives.js
+++ b/js-assembler/runtime-src/baselib-primitives.js
@@ -1465,8 +1465,8 @@
 	    var i;
             if (MACHINE.argcount === 1) {
                 var sym = checkSymbol(MACHINE, 'error', 1);
-                // FIXME: we should collect the current continuation marks here...
-                raise(MACHINE, baselib.exceptions.makeExnFail(String(sym), undefined));
+                raise(MACHINE, baselib.exceptions.makeExnFail(String(sym), 
+                                                              MACHINE.captureContinuationMarks()));
             } 
             
             if (isString(MACHINE.env[MACHINE.env.length - 1])) {
@@ -1477,7 +1477,7 @@
                 raise(MACHINE, baselib.exceptions.makeExnFail(String(MACHINE.env[MACHINE.env.length - 1]) +
                                                               ": " +
                                                               vs.join(' '),
-                                                              undefined));
+                                                              MACHINE.captureContinuationMarks()));
             }
 
             if (isSymbol(MACHINE.env[MACHINE.env.length - 1])) {
@@ -1489,7 +1489,7 @@
                 raise(MACHINE, baselib.exceptions.makeExnFail(
                     baselib.format.format('~s: ' + String(fmtString),
                                           args),
-                    undefined));
+                    MACHINE.captureContinuationMarks()));
             }
 
             // Fall-through
@@ -1509,7 +1509,7 @@
                                       [name,
                                        message,
                                        val]),
-                undefined));
+                MACHINE.captureContinuationMarks()));
         });