diff --git a/flake8_mypy.py b/flake8_mypy.py
index 5560f2b..0577ec6 100644
--- a/flake8_mypy.py
+++ b/flake8_mypy.py
@@ -183,15 +183,26 @@ def run(self) -> Iterator[_Flake8Error]:
         # Always put the file in a separate temporary directory to avoid
         # unexpected clashes with other .py and .pyi files in the same original
         # directory.
-        with TemporaryDirectory(prefix='flake8mypy_') as d:
-            with NamedTemporaryFile(
-                'w', encoding='utf8', prefix='tmpmypy_', suffix='.py', dir=d
-            ) as f:
-                self.filename = f.name
-                for line in self.lines:
-                    f.write(line)
-                f.flush()
-                yield from self._run()
+        try:
+            with TemporaryDirectory(prefix='flake8mypy_') as d:
+                with NamedTemporaryFile(
+                    'wt', prefix='tmpmypy_', suffix='.py', dir=d
+                ) as f:
+                    self.filename = f.name
+                    for line in self.lines:
+                        f.write(line)
+                    f.flush()
+                    yield from self._run()
+        except UnicodeEncodeError:
+            with TemporaryDirectory(prefix='flake8mypy_') as d:
+                with NamedTemporaryFile(
+                    'wb', prefix='tmpmypy_', suffix='.py', dir=d
+                ) as f:
+                    self.filename = f.name
+                    for line in self.lines:
+                        f.write(line.encode(r'utf8'))
+                    f.flush()
+                    yield from self._run()
 
     def _run(self) -> Iterator[_Flake8Error]:
         mypy_cmdline = self.build_mypy_cmdline(self.filename, self.options.mypy_config)