diff --git a/src/tox/_pytestplugin.py b/src/tox/_pytestplugin.py
index 14d166bd6..7637880ff 100644
--- a/src/tox/_pytestplugin.py
+++ b/src/tox/_pytestplugin.py
@@ -176,9 +176,13 @@ def outlines(self):
         return err + out
 
     def __repr__(self):
-        return "RunResult(ret={}, args={}, out=\n{}\n, err=\n{})".format(
-            self.ret, " ".join(str(i) for i in self.args), self.out, self.err
+        res = "RunResult(ret={}, args={!r}, out=\n{}\n, err=\n{})".format(
+            self.ret, self.args, self.out, self.err
         )
+        if six.PY2:
+            return res.encode("UTF-8")
+        else:
+            return res
 
     def output(self):
         return "{}\n{}\n{}".format(self.ret, self.err, self.out)
diff --git a/tests/unit/test_pytest_plugins.py b/tests/unit/test_pytest_plugins.py
index 873731b02..dcb6e3a06 100644
--- a/tests/unit/test_pytest_plugins.py
+++ b/tests/unit/test_pytest_plugins.py
@@ -4,11 +4,12 @@
 
 """
 import os
+import sys
 
 import py.path
 import pytest
 
-from tox._pytestplugin import _filedefs_contains, _path_parts
+from tox._pytestplugin import RunResult, _filedefs_contains, _path_parts
 
 
 class TestInitProj:
@@ -111,3 +112,15 @@ def test_on_py_path(self):
 )
 def test_filedefs_contains(base, filedefs, target, expected):
     assert bool(_filedefs_contains(base, filedefs, target)) == expected
+
+
+def test_run_result_repr(capfd):
+    with RunResult(["hello", "world"], capfd) as run_result:
+        # simulate tox writing some unicode output
+        stdout_buffer = getattr(sys.stdout, "buffer", sys.stdout)
+        stdout_buffer.write(u"\u2603".encode("UTF-8"))
+
+    # must not `UnicodeError` on repr(...)
+    ret = repr(run_result)
+    # must be native `str`, (bytes in py2, str in py3)
+    assert isinstance(ret, str)