diff --git a/interpreter/script/js.ml b/interpreter/script/js.ml
index 6d70f1fb6a..b0be4384b1 100644
--- a/interpreter/script/js.ml
+++ b/interpreter/script/js.ml
@@ -53,7 +53,7 @@ function register(name, instance) {
   registry[name] = instance.exports;
 }
 
-function module(bytes, valid = true) {
+function module(bytes, loc, valid = true) {
   let buffer = new ArrayBuffer(bytes.length);
   let view = new Uint8Array(buffer);
   for (let i = 0; i < bytes.length; ++i) {
@@ -92,8 +92,8 @@ function run(action) {
   action();
 }
 
-function assert_malformed(bytes) {
-  try { module(bytes, false) } catch (e) {
+function assert_malformed(bytes, loc) {
+  try { module(bytes, loc, false) } catch (e) {
     if (e instanceof WebAssembly.CompileError) return;
   }
   throw new Error("Wasm decoding failure expected");
@@ -103,8 +103,8 @@ function assert_malformed_custom(bytes) {
   return;
 }
 
-function assert_invalid(bytes) {
-  try { module(bytes, false) } catch (e) {
+function assert_invalid(bytes, loc) {
+  try { module(bytes, loc, false) } catch (e) {
     if (e instanceof WebAssembly.CompileError) return;
   }
   throw new Error("Wasm validation failure expected");
@@ -128,7 +128,7 @@ function assert_uninstantiable(mod) {
   throw new Error("Wasm trap expected");
 }
 
-function assert_trap(action) {
+function assert_trap(action, loc) {
   try { action() } catch (e) {
     if (e instanceof WebAssembly.RuntimeError) return;
   }
@@ -150,7 +150,7 @@ function assert_exhaustion(action) {
   throw new Error("Wasm resource exhaustion expected");
 }
 
-function assert_return(action, ...expected) {
+function assert_return(action, loc, ...expected) {
   let actual = action();
   if (actual === undefined) {
     actual = [];
@@ -749,7 +749,7 @@ let rec of_definition def =
 let of_wrapper env x_opt name wrap_action wrap_assertion at =
   let x = of_inst_opt env x_opt in
   let bs = wrap name wrap_action wrap_assertion at in
-  "call(instance(module(" ^ of_bytes bs ^ "), " ^
+  "call(instance(module(" ^ of_bytes bs ^ ", \"wrapper\"), " ^
     "exports(" ^ x ^ ")), " ^ " \"run\", [])"
 
 let of_action env act =
@@ -775,9 +775,9 @@ let of_action env act =
     | _ -> None
     )
 
-let of_assertion' env act name args wrapper_opt =
+let of_assertion' env act loc name args wrapper_opt =
   let act_js, act_wrapper_opt = of_action env act in
-  let js = name ^ "(() => " ^ act_js ^ String.concat ", " ("" :: args) ^ ")" in
+  let js = name ^ "(() => " ^ act_js ^ loc ^ String.concat ", " ("" :: args) ^ ")" in
   match act_wrapper_opt with
   | None -> js ^ ";"
   | Some (act_wrapper, out) ->
@@ -785,35 +785,40 @@ let of_assertion' env act name args wrapper_opt =
       match wrapper_opt with
       | None -> name, run
       | Some wrapper -> "run", wrapper
-    in run_name ^ "(() => " ^ act_wrapper (wrapper out) act.at ^ ");  // " ^ js
+    in run_name ^ "(() => " ^ act_wrapper (wrapper out) act.at ^ loc ^ ");  // " ^ js
 
 let of_assertion env ass =
+  let loc = Filename.basename ass.at.left.file ^
+    ":" ^ string_of_int ass.at.left.line in
+  let loc_as_arg = ", \"" ^ String.escaped loc ^ "\"" in
   match ass.it with
   | AssertMalformed (def, _) ->
-    "assert_malformed(" ^ of_definition def ^ ");"
+    "assert_malformed(" ^ of_definition def ^ loc_as_arg ^ ");"
   | AssertMalformedCustom (def, _) ->
-    "assert_malformed_custom(" ^ of_definition def ^ ");"
+    "assert_malformed_custom(" ^ of_definition def ^ loc_as_arg ^ ");"
   | AssertInvalid (def, _) ->
-    "assert_invalid(" ^ of_definition def ^ ");"
+    "assert_invalid(" ^ of_definition def ^ loc_as_arg ^ ");"
   | AssertInvalidCustom (def, _) ->
-    "assert_invalid_custom(" ^ of_definition def ^ ");"
+    "assert_invalid_custom(" ^ of_definition def ^ loc_as_arg ^ ");"
   | AssertUnlinkable (x_opt, _) ->
     "assert_unlinkable(" ^ of_mod_opt env x_opt ^ ");"
   | AssertUninstantiable (x_opt, _) ->
     "assert_uninstantiable(" ^ of_mod_opt env x_opt ^ ");"
   | AssertReturn (act, ress) ->
-    of_assertion' env act "assert_return" (List.map of_result ress)
+    of_assertion' env act loc_as_arg "assert_return" (List.map of_result ress)
       (Some (assert_return ress))
   | AssertTrap (act, _) ->
-    of_assertion' env act "assert_trap" [] None
+    of_assertion' env act loc_as_arg "assert_trap" [] None
   | AssertExhaustion (act, _) ->
-    of_assertion' env act "assert_exhaustion" [] None
+    of_assertion' env act loc_as_arg "assert_exhaustion" [] None
   | AssertException act ->
-    of_assertion' env act "assert_exception" [] None
+    of_assertion' env act loc_as_arg "assert_exception" [] None
 
 let of_command env cmd =
-  "\n// " ^ Filename.basename cmd.at.left.file ^
-    ":" ^ string_of_int cmd.at.left.line ^ "\n" ^
+  let loc = String.escaped (Filename.basename cmd.at.left.file ^
+    ":" ^ string_of_int cmd.at.left.line) in
+  let loc_as_arg = ", \"" ^ loc ^ "\"" in
+  "\n// " ^ loc ^ "\n" ^
   match cmd.it with
   | Module (x_opt, def) ->
     let rec unquote def =
@@ -823,7 +828,7 @@ let of_command env cmd =
       | Quoted (_, s) ->
         unquote (snd (Parse.Module.parse_string ~offset:s.at s.it))
     in bind_mod env x_opt (unquote def);
-    "let " ^ current_mod env ^ " = module(" ^ of_definition def ^ ");\n" ^
+    "let " ^ current_mod env ^ " = module(" ^ of_definition def ^ loc_as_arg ^ ");\n" ^
     (if x_opt = None then "" else
     "let " ^ of_mod_opt env x_opt ^ " = " ^ current_mod env ^ ";\n")
   | Instance (x1_opt, x2_opt) ->
@@ -835,7 +840,7 @@ let of_command env cmd =
   | Register (name, x_opt) ->
     "register(" ^ of_name name ^ ", " ^ of_inst_opt env x_opt ^ ")\n"
   | Action act ->
-    of_assertion' env act "run" [] None ^ "\n"
+    of_assertion' env act loc_as_arg "run" [] None ^ "\n"
   | Assertion ass ->
     of_assertion env ass ^ "\n"
   | Meta _ -> assert false
diff --git a/test/harness/async_index.js b/test/harness/async_index.js
index 8a01b21211..7b4fcd1ae4 100644
--- a/test/harness/async_index.js
+++ b/test/harness/async_index.js
@@ -150,10 +150,10 @@ function binary(bytes) {
 /**
  * Returns a compiled module, or throws if there was an error at compilation.
  */
-function module(bytes, valid = true) {
-  const test = valid
-    ? "Test that WebAssembly compilation succeeds"
-    : "Test that WebAssembly compilation fails";
+function module(bytes, source, valid = true) {
+  const test = `${ valid ? "Test that WebAssembly compilation succeeds" :
+                "Test that WebAssembly compilation fails"} (${source})`;
+
   const loc = new Error().stack.toString().replace("Error", "");
   let buffer = binary(bytes);
   let validated = WebAssembly.validate(buffer);
@@ -167,6 +167,7 @@ function module(bytes, valid = true) {
       uniqueTest(_ => {
         assert_true(valid, loc);
       }, test);
+      module.source = source;
       return module;
     },
     error => {
@@ -181,26 +182,27 @@ function module(bytes, valid = true) {
   return chain;
 }
 
-function assert_invalid(bytes) {
-  module(bytes, EXPECT_INVALID);
+function assert_invalid(bytes, source) {
+  module(bytes, source, EXPECT_INVALID);
 }
 
 const assert_malformed = assert_invalid;
 
-function assert_invalid_custom(bytes) {
-  module(bytes);
+function assert_invalid_custom(bytes, source) {
+  module(bytes, source);
 }
 
 const assert_malformed_custom = assert_invalid_custom;
 
 function instance(module, imports, valid = true) {
-  const test = valid
+  let test = valid
     ? "Test that WebAssembly instantiation succeeds"
     : "Test that WebAssembly instantiation fails";
   const loc = new Error().stack.toString().replace("Error", "");
   chain = Promise.all([module, imports, chain])
     .then(values => {
       let imports = values[1] ? values[1] : registry;
+      test += ` (${values[0].source})`;
       return WebAssembly.instantiate(values[0], imports);
     })
     .then(
@@ -235,8 +237,8 @@ function call(instance, name, args) {
   });
 }
 
-function run(action) {
-  const test = "Run a WebAssembly test without special assertions";
+function run(action, source) {
+  const test = `Run a WebAssembly test without special assertions (${source})`;
   const loc = new Error().stack.toString().replace("Error", "");
   chain = Promise.all([chain, action()])
     .then(
@@ -256,8 +258,8 @@ function run(action) {
     .catch(_ => {});
 }
 
-function assert_trap(action) {
-  const test = "Test that a WebAssembly code traps";
+function assert_trap(action, source) {
+  const test = `Test that a WebAssembly code traps (${source})`;
   const loc = new Error().stack.toString().replace("Error", "");
   chain = Promise.all([chain, action()])
     .then(
@@ -279,8 +281,8 @@ function assert_trap(action) {
     .catch(_ => {});
 }
 
-function assert_return(action, ...expected) {
-  const test = "Test that a WebAssembly code returns a specific result";
+function assert_return(action, source, ...expected) {
+  const test = `Test that a WebAssembly code returns a specific result (${source})`;
   const loc = new Error().stack.toString().replace("Error", "");
   chain = Promise.all([action(), chain])
     .then(
diff --git a/test/harness/sync_index.js b/test/harness/sync_index.js
index 5c4549be2e..77f601f590 100644
--- a/test/harness/sync_index.js
+++ b/test/harness/sync_index.js
@@ -150,7 +150,7 @@ function binary(bytes) {
 /**
  * Returns a compiled module, or throws if there was an error at compilation.
  */
-function module(bytes, valid = true) {
+function module(bytes, source, valid = true) {
     let buffer = binary(bytes);
     let validated;
 
@@ -176,6 +176,7 @@ function module(bytes, valid = true) {
     let module;
     try {
         module = new WebAssembly.Module(buffer);
+        module.source = source;
     } catch(e) {
         if (valid)
             throw new Error('WebAssembly.Module ctor unexpectedly throws ${typeof e}: ${e}${e.stack}');
@@ -189,32 +190,32 @@ function uniqueTest(func, desc) {
     test(func, testNum() + desc);
 }
 
-function assert_invalid(bytes) {
+function assert_invalid(bytes, source) {
     uniqueTest(() => {
         try {
-            module(bytes, /* valid */ false);
+            module(bytes, source, /* valid */ false);
             throw new Error('did not fail');
         } catch(e) {
             assert_true(e instanceof WebAssembly.CompileError, "expected invalid failure:");
         }
-    }, "A wast module that should be invalid or malformed.");
+    }, `A wast module that should be invalid or malformed. (${source})`);
 }
 
 const assert_malformed = assert_invalid;
 
-function assert_invalid_custom(bytes) {
+function assert_invalid_custom(bytes, source) {
     uniqueTest(() => {
         try {
-            module(bytes, /* valid */ true);
+            module(bytes, source, /* valid */ true);
         } catch(e) {
             throw new Error('failed on custom section error');
         }
-    }, "A wast module that should have an invalid or malformed custom section.");
+    }, `A wast module that should have an invalid or malformed custom section. (${source})`);
 }
 
 const assert_malformed_custom = assert_invalid_custom;
 
-function instance(mod, imports = registry, valid = true) {
+function instance(module, imports = registry, valid = true) {
     if (imports instanceof Result) {
         if (imports.isError())
             return imports;
@@ -225,7 +226,7 @@ function instance(mod, imports = registry, valid = true) {
 
     let i;
     try {
-        i = new WebAssembly.Instance(mod, imports);
+        i = new WebAssembly.Instance(module, imports);
     } catch(e) {
         err = e;
     }
@@ -234,7 +235,7 @@ function instance(mod, imports = registry, valid = true) {
         uniqueTest(() => {
             let instantiated = err === null;
             assert_true(instantiated, err);
-        }, "module successfully instantiated");
+        }, `module successfully instantiated (${module.source})`);
     }
 
     return err !== null ? ErrorResult(err) : ValueResult(i);
@@ -285,7 +286,7 @@ function exports(instance) {
     return ValueResult({ module: instance.value.exports, spectest: registry.spectest });
 }
 
-function run(action) {
+function run(action, source) {
     let result = action();
 
     _assert(result instanceof Result);
@@ -293,7 +294,7 @@ function run(action) {
     uniqueTest(() => {
         if (result.isError())
             throw result.value;
-    }, "A wast test that runs without any special assertion.");
+    }, `A wast test that runs without any special assertion. (${source})`);
 }
 
 function assert_unlinkable(bytes) {
@@ -324,7 +325,7 @@ function assert_uninstantiable(bytes) {
     }, "A wast module that is uninstantiable.");
 }
 
-function assert_trap(action) {
+function assert_trap(action, source) {
     let result = action();
 
     _assert(result instanceof Result);
@@ -335,7 +336,7 @@ function assert_trap(action) {
             let e = result.value;
             assert_true(e instanceof WebAssembly.RuntimeError, `expected runtime error, observed ${e}:`);
         }
-    }, "A wast module that must trap at runtime.");
+    }, `A wast module that must trap at runtime. (${source})`);
 }
 
 let StackOverflow;
@@ -355,7 +356,7 @@ function assert_exhaustion(action) {
     }, "A wast module that must exhaust the stack space.");
 }
 
-function assert_return(action, ...expected) {
+function assert_return(action, source, ...expected) {
     let result = action();
     _assert(result instanceof Result);
 
@@ -408,7 +409,7 @@ function assert_return(action, ...expected) {
                     assert_equals(actual[i], expected[i]);
             }
         }
-    }, "A wast module that must return a particular value.");
+    }, `A wast module that must return a particular value. (${source})`);
 }
 
 function assert_return_nan(action) {