diff --git a/changelog/6871.bugfix.rst b/changelog/6871.bugfix.rst
new file mode 100644
index 00000000000..fe69c750915
--- /dev/null
+++ b/changelog/6871.bugfix.rst
@@ -0,0 +1 @@
+Fix crash with captured output when using the :fixture:`capsysbinary fixture <capsysbinary>`.
diff --git a/src/_pytest/capture.py b/src/_pytest/capture.py
index 1df4667907c..5e79711c2ca 100644
--- a/src/_pytest/capture.py
+++ b/src/_pytest/capture.py
@@ -682,7 +682,8 @@ def resume(self):
         setattr(sys, self.name, self.tmpfile)
         self._state = "resumed"
 
-    def writeorg(self, data):
+    def writeorg(self, data: str) -> None:
+        data = data.decode(self._old.encoding)
         self._old.write(data)
         self._old.flush()
 
@@ -696,6 +697,10 @@ def snap(self):
         self.tmpfile.truncate()
         return res
 
+    def writeorg(self, data: str) -> None:
+        self._old.write(data)
+        self._old.flush()
+
 
 class TeeSysCapture(SysCapture):
     def __init__(self, fd, tmpfile=None):
diff --git a/testing/test_capture.py b/testing/test_capture.py
index d30d796d0c2..2303fd2cac0 100644
--- a/testing/test_capture.py
+++ b/testing/test_capture.py
@@ -542,18 +542,33 @@ def test_hello(capfdbinary):
         reprec.assertoutcome(passed=1)
 
     def test_capsysbinary(self, testdir):
-        reprec = testdir.inline_runsource(
+        p1 = testdir.makepyfile(
             """\
             def test_hello(capsysbinary):
                 import sys
+
                 # some likely un-decodable bytes
                 sys.stdout.buffer.write(b'\\xfe\\x98\\x20')
+
                 out, err = capsysbinary.readouterr()
                 assert out == b'\\xfe\\x98\\x20'
                 assert err == b''
+
+                # handles writing strings
+                print("hello")
+                print("hello stderr", file=sys.stderr)
             """
         )
-        reprec.assertoutcome(passed=1)
+        result = testdir.runpytest(str(p1), "-rA")
+        result.stdout.fnmatch_lines(
+            [
+                "*- Captured stdout call -*",
+                "hello",
+                "*- Captured stderr call -*",
+                "hello stderr",
+                "*= 1 passed in *",
+            ]
+        )
 
     def test_partial_setup_failure(self, testdir):
         p = testdir.makepyfile(