diff --git a/ui/frontend/.eslintrc.js b/ui/frontend/.eslintrc.js
index 92d5fe370..de16ebb19 100644
--- a/ui/frontend/.eslintrc.js
+++ b/ui/frontend/.eslintrc.js
@@ -97,6 +97,7 @@ module.exports = {
         'reducers/selection.ts',
         'reducers/versions.ts',
         'reducers/websocket.ts',
+        'selectors/index.spec.ts',
         'types.ts',
         'websocketActions.ts',
         'websocketMiddleware.ts',
diff --git a/ui/frontend/.prettierignore b/ui/frontend/.prettierignore
index 543e3cee9..ed34c38c6 100644
--- a/ui/frontend/.prettierignore
+++ b/ui/frontend/.prettierignore
@@ -48,6 +48,7 @@ node_modules
 !reducers/selection.ts
 !reducers/versions.ts
 !reducers/websocket.ts
+!selectors/index.spec.ts
 !types.ts
 !websocketActions.ts
 !websocketMiddleware.ts
diff --git a/ui/frontend/selectors/index.spec.ts b/ui/frontend/selectors/index.spec.ts
index bc443e3b4..98d1f51bf 100644
--- a/ui/frontend/selectors/index.spec.ts
+++ b/ui/frontend/selectors/index.spec.ts
@@ -1,60 +1,66 @@
 import reducer from '../reducers';
 import { editCode } from '../reducers/code';
-
 import { hasMainFunctionSelector } from './index';
 
-const buildState = (code: string) => {
-  const state = reducer(undefined, editCode(code));
-  return state;
-};
+const buildState = (code: string) => reducer(undefined, editCode(code));
+
+const doMainFunctionSelector = (code: string) => hasMainFunctionSelector(buildState(code));
 
 describe('checking for a main function', () => {
   test('empty code has no main', () => {
-    expect(hasMainFunctionSelector(buildState(''))).toBe(false);
+    expect(doMainFunctionSelector('')).toBe(false);
   });
 
   test('a plain main counts', () => {
-    expect(hasMainFunctionSelector(buildState('fn main()'))).toBe(true);
+    expect(doMainFunctionSelector('fn main()')).toBe(true);
   });
 
   test('a public main counts', () => {
-    expect(hasMainFunctionSelector(buildState('pub fn main()'))).toBe(true);
+    expect(doMainFunctionSelector('pub fn main()')).toBe(true);
   });
 
   test('an async main counts', () => {
-    expect(hasMainFunctionSelector(buildState('async fn main()'))).toBe(true);
+    expect(doMainFunctionSelector('async fn main()')).toBe(true);
   });
 
   test('a public async main counts', () => {
-    expect(hasMainFunctionSelector(buildState('pub async fn main()'))).toBe(true);
+    expect(doMainFunctionSelector('pub async fn main()')).toBe(true);
   });
 
   test('a const main counts', () => {
-    expect(hasMainFunctionSelector(buildState('const fn main()'))).toBe(true);
+    expect(doMainFunctionSelector('const fn main()')).toBe(true);
   });
 
   test('a public const main counts', () => {
-    expect(hasMainFunctionSelector(buildState('pub const fn main()'))).toBe(true);
+    expect(doMainFunctionSelector('pub const fn main()')).toBe(true);
   });
 
   test('a public const async main counts', () => {
-    expect(hasMainFunctionSelector(buildState('pub const async fn main()'))).toBe(true);
+    expect(doMainFunctionSelector('pub const async fn main()')).toBe(true);
   });
 
   test('leading indentation is ignored', () => {
-    expect(hasMainFunctionSelector(buildState('\t fn main()'))).toBe(true);
+    expect(doMainFunctionSelector('\t fn main()')).toBe(true);
   });
 
   test('extra space everywhere is ignored', () => {
-    expect(hasMainFunctionSelector(buildState('  pub async   fn  main  (  )'))).toBe(true);
+    expect(doMainFunctionSelector('  pub async   fn  main  (  )')).toBe(true);
   });
 
   test('a commented-out main does not count', () => {
-    expect(hasMainFunctionSelector(buildState('// fn main()'))).toBe(false);
-    expect(hasMainFunctionSelector(buildState('/* fn main()'))).toBe(false);
+    expect(doMainFunctionSelector('// fn main()')).toBe(false);
+    expect(doMainFunctionSelector('/* fn main()')).toBe(false);
   });
 
   test('a function with the substring main does not count', () => {
-    expect(hasMainFunctionSelector(buildState('fn mainly()'))).toBe(false);
+    expect(doMainFunctionSelector('fn mainly()')).toBe(false);
+  });
+
+  test('a main function after other items on the same line', () => {
+    expect(doMainFunctionSelector('use std; fn main(){ println!("Hello, world!"); }')).toBe(true);
+  });
+
+  test('a main function with a block comment in the argument list', () => {
+    expect(doMainFunctionSelector('fn main(/* comment */) {')).toBe(true);
   });
 });
diff --git a/ui/frontend/selectors/index.ts b/ui/frontend/selectors/index.ts
index 462e1676a..0fcfa92f6 100644
--- a/ui/frontend/selectors/index.ts
+++ b/ui/frontend/selectors/index.ts
@@ -20,7 +20,15 @@ export const selectionSelector = (state: State) => state.selection;
 const HAS_TESTS_RE = /^\s*#\s*\[\s*test\s*([^"]*)]/m;
 export const hasTestsSelector = createSelector(codeSelector, code => !!code.match(HAS_TESTS_RE));
 
-const HAS_MAIN_FUNCTION_RE = /^\s*(pub\s+)?\s*(const\s+)?\s*(async\s+)?\s*fn\s+main\s*\(\s*\)/m;
+// https://stackoverflow.com/a/34755045/155423
+const HAS_MAIN_FUNCTION_RE = new RegExp(
+  [
+    /^([^\n\r\/]*;)?/,
+    /\s*(pub\s+)?\s*(const\s+)?\s*(async\s+)?\s*/,
+    /fn\s+main\s*\(\s*(\/\*.*\*\/)?\s*\)/,
+  ].map((r) => r.source).join(''),
+  'm'
+);
 export const hasMainFunctionSelector = createSelector(codeSelector, code => !!code.match(HAS_MAIN_FUNCTION_RE));
 
 const CRATE_TYPE_RE = /^\s*#!\s*\[\s*crate_type\s*=\s*"([^"]*)"\s*]/m;