diff --git a/js-assembler/package.rkt b/js-assembler/package.rkt
index f554935..b1ecb3a 100644
--- a/js-assembler/package.rkt
+++ b/js-assembler/package.rkt
@@ -597,7 +597,7 @@ var invokeMainModule = function() {
             }
         },
         function(M, e) {
-            var contMarkSet, context, i, appName;
+            var contMarkSet, context, i, appName, contextDiv;
             // On main module invokation failure
             if (window.console && window.console.log) {
                 window.console.log(e.stack || e);
@@ -609,30 +609,39 @@ var invokeMainModule = function() {
             if (e.hasOwnProperty('racketError') &&
                 plt.baselib.exceptions.isExn(e.racketError)) {
                 contMarkSet = plt.baselib.exceptions.exnContMarks(e.racketError);
+                contextDiv = $('<div/>');
+
+                if (e.racketError.structType &&
+                    plt.baselib.structs.supportsStructureTypeProperty(
+                        e.racketError.structType,
+                        plt.baselib.structs.propExnSrcloc)) {
+
+
+                }
+
                 if (contMarkSet) {
                     context = contMarkSet.getContext(M);
                     for (i = 0; i < context.length; i++) {
                         if (plt.runtime.isVector(context[i])) {
-                            M.params.currentErrorDisplayer(
-                                M,
-                                $('<div/>').text('  at ' + context[i].elts[0] +
+                                $('<div/>').text('at ' + context[i].elts[0] +
                                                  ', line ' + context[i].elts[2] +
                                                  ', column ' + context[i].elts[3])
                                     .addClass('stacktrace')
                                     .css('margin-left', '10px')
                                     .css('whitespace', 'pre')
-                                    .css('color', 'red'));
+                                    .css('color', 'red')
+                                    .appendTo(contextDiv);
                         } else if (plt.runtime.isProcedure(context[i])) {
-                            M.params.currentErrorDisplayer(
-                                M,
-                                $('<div/>').text('  in ' + context[i].displayName)
+                            $('<div/>').text('in ' + context[i].displayName)
                                     .addClass('stacktrace')
                                     .css('margin-left', '10px')
                                     .css('whitespace', 'pre')
-                                    .css('color', 'red'));
+                                    .css('color', 'red')
+                                    .appendTo(contextDiv);
                         }                                     
                     }
                 }
+                M.params.currentErrorDisplayer(M, contextDiv);
             }
         });
 };
diff --git a/js-assembler/runtime-src/baselib-primitives.js b/js-assembler/runtime-src/baselib-primitives.js
index 9ce936b..110a6ed 100644
--- a/js-assembler/runtime-src/baselib-primitives.js
+++ b/js-assembler/runtime-src/baselib-primitives.js
@@ -2088,7 +2088,7 @@
 
     installPrimitiveConstant(
         'prop:exn:srclocs',
-        "fixme");
+        baselib.structs.propExnSrcloc);
 
 
     installPrimitiveProcedure(
diff --git a/js-assembler/runtime-src/baselib-structs.js b/js-assembler/runtime-src/baselib-structs.js
index 08c5b0a..edfd807 100644
--- a/js-assembler/runtime-src/baselib-structs.js
+++ b/js-assembler/runtime-src/baselib-structs.js
@@ -9,9 +9,10 @@
 
     //////////////////////////////////////////////////////////////////////
 
-    var Struct = function (constructorName, fields) {
+    var Struct = function (constructorName, fields, structType) {
         this._constructorName = constructorName; 
         this._fields = [];
+        this.structType = structType;
     };
 
     Struct.prototype.toWrittenString = function (cache) { 
@@ -147,9 +148,9 @@
 
         // RawConstructor creates a new struct type inheriting from
         // the parent, with no guard checks.
-        var RawConstructor = function (name, args) {
+        var RawConstructor = function (name, args, structType) {
             var i;
-            parentType.type.call(this, name, args);
+            parentType.type.call(this, name, args, structType);
             for (i = 0; i < initFieldCnt; i++) {
                 this._fields.push(args[i+parentType.numberOfArgs]);
             }
@@ -192,7 +193,7 @@
                     args,
                     baselib.symbols.Symbol.makeInstance(theName),
                     function (res) { 
-                        return new RawConstructor(theName, res); });
+                        return new RawConstructor(theName, res, newType); });
             },
 
             // predicate
diff --git a/tests/more-tests/sigs-cs019.rkt b/tests/more-tests/sigs-cs019.rkt
index 4a46706..224d485 100755
--- a/tests/more-tests/sigs-cs019.rkt
+++ b/tests/more-tests/sigs-cs019.rkt
@@ -19,6 +19,7 @@
 
 (define: (g [x : Number$]) -> String$ "x")
 (check-expect (g 10) "x")
+(g "x")
 #;(check-error (g "x"))
 #;(check-violation-highlights
  (g "x")