diff --git a/src/ast_utils.js b/src/ast_utils.js
index 017cf82..375603b 100644
--- a/src/ast_utils.js
+++ b/src/ast_utils.js
@@ -170,7 +170,18 @@ export const find_node = (node, pred) => {
 export const find_error_origin_node = node =>
   find_node(
     node, 
-    n => n.result != null && !n.result.ok && n.result.error != null
+    n => n.result != null && !n.result.ok && (
+      n.result.error != null
+      ||
+      // In case if throw null or throw undefined
+      n.type == 'throw'
+      ||
+      // await can also throw null
+      n.type == 'unary' && n.operator == 'await'
+      // or function call throwing null or undefined
+      || 
+      n.type == 'function_call'
+    )
   )
 
 /* Maps tree nodes, discarding mapped children, so maps only node contents, not
diff --git a/src/calltree.js b/src/calltree.js
index 048aba4..9483471 100644
--- a/src/calltree.js
+++ b/src/calltree.js
@@ -36,10 +36,10 @@ export const set_location = (state, location) => set_cursor_position(
 
 const is_stackoverflow = node =>
   // Chrome
-  node.error.message == 'Maximum call stack size exceeded'
+  node.error?.message == 'Maximum call stack size exceeded'
   ||
   // Firefox
-  node.error.message == "too much recursion"
+  node.error?.message == "too much recursion"
 
 export const calltree_node_loc = node => node.toplevel  
     ? {module: node.module}
diff --git a/src/editor/calltree.js b/src/editor/calltree.js
index eba7f89..856859a 100644
--- a/src/editor/calltree.js
+++ b/src/editor/calltree.js
@@ -115,7 +115,7 @@ export class CallTree {
             el('i', '', 
               'toplevel: ' + (n.module == '' ? '*scratch*' : n.module),
             ),
-            n.ok ? '' : el('span', 'call_header error', '\xa0', n.error.toString()),
+            n.ok ? '' : el('span', 'call_header error', '\xa0', stringify_for_header(n.error)),
           )
         : el('span', 
               'call_header ' 
@@ -135,7 +135,7 @@ export class CallTree {
              ),
             ')' ,
             // TODO: show error message only where it was thrown, not every frame?
-            ': ', (n.ok ? stringify_for_header(n.value) : n.error.toString()) 
+            ': ', (n.ok ? stringify_for_header(n.value) : stringify_for_header(n.error)) 
           ),
       ),
       (n.children == null || !is_expanded)
diff --git a/src/editor/editor.js b/src/editor/editor.js
index b4c0257..9ede59e 100644
--- a/src/editor/editor.js
+++ b/src/editor/editor.js
@@ -1,5 +1,5 @@
 import {exec, get_state} from '../index.js'
-import {ValueExplorer} from './value_explorer.js'
+import {ValueExplorer, stringify_for_header} from './value_explorer.js'
 import {el, stringify, fn_link} from './domutils.js'
 import {FLAGS} from '../feature_flags.js'
 
@@ -244,7 +244,7 @@ export class Editor {
 
       exp.render(value)
     } else {
-      content.appendChild(el('span', 'eval_error', error.toString()))
+      content.appendChild(el('span', 'eval_error', stringify_for_header(error)))
     }
 
     this.widget = {
diff --git a/test/test.js b/test/test.js
index 4a5735a..01c28c4 100644
--- a/test/test.js
+++ b/test/test.js
@@ -456,6 +456,21 @@ export const tests = [
     )
   }),
 
+  test('throw null', () => {
+    assert_code_error(`throw null`, null)
+  }),
+
+  test('throw null from function', () => {
+    const code = `
+      const throws = () => { throw null }
+      throws()
+    `
+    const s = test_initial_state(code)
+    const moved = COMMANDS.move_cursor(s, code.indexOf('throws()'))
+    assert_equal(moved.value_explorer.result.ok, false)
+    assert_equal(moved.value_explorer.result.error, null)
+  }),
+
   test('new', () => {
     assert_code_evals_to('new Error("test").message', 'test')
   }),
@@ -2774,6 +2789,13 @@ const y = x()`
     )
   }),
 
+  test('async/await promise rejected with null', async () => {
+    await assert_code_error_async(
+      `await Promise.reject()`,
+      undefined
+    )
+  }),
+
   test('async/await await rejected Promise returned from async', async () => {
     await assert_code_error_async(
       `
diff --git a/test/utils.js b/test/utils.js
index d79b5e3..abad6f7 100644
--- a/test/utils.js
+++ b/test/utils.js
@@ -1,5 +1,4 @@
-import {parse, print_debug_node, load_modules} from '../src/parse_js.js'
-import {eval_tree, eval_frame} from '../src/eval.js'
+import {print_debug_node, load_modules} from '../src/parse_js.js'
 import {active_frame, pp_calltree} from '../src/calltree.js'
 import {COMMANDS} from '../src/cmd.js'
 
@@ -17,21 +16,18 @@ export const parse_modules = (entry, modules) =>
   load_modules(entry, module_name => modules[module_name])
 
 export const assert_code_evals_to = (codestring, expected) => {
-  const parse_result = parse(codestring)
-  assert_equal(parse_result.ok, true)
-  const tree = eval_tree(parse_result.node)
-  const frame = eval_frame(tree)
+  const s = test_initial_state(codestring)
+  const frame = active_frame(s)
   const result = frame.children.at(-1).result
-  assert_equal({ok: result.ok, value: result.value}, {ok: true, value: expected})
+  assert_equal(result.ok, true)
+  assert_equal(result.value, expected)
   return frame
 }
 
 export const assert_code_error = (codestring, error) => {
-  const parse_result = parse(codestring)
-  assert_equal(parse_result.ok, true)
-  const tree = eval_tree(parse_result.node)
-  const frame = eval_frame(tree)
-  const result = frame.children[frame.children.length - 1].result
+  const state = test_initial_state(codestring)
+  const frame = active_frame(state)
+  const result = frame.children.at(-1).result
   assert_equal(result.ok, false)
   assert_equal(result.error, error)
 }