diff --git a/git/compat.py b/git/compat.py
index a0aea1ac4..c9b83ba46 100644
--- a/git/compat.py
+++ b/git/compat.py
@@ -18,7 +18,7 @@
 
 # typing --------------------------------------------------------------------
 
-from typing import Any, AnyStr, Dict, Optional, Type
+from typing import IO, Any, AnyStr, Dict, Optional, Type, Union
 from git.types import TBD
 
 # ---------------------------------------------------------------------------
@@ -30,7 +30,7 @@
 defenc = sys.getfilesystemencoding()
 
 
-def safe_decode(s: Optional[AnyStr]) -> Optional[str]:
+def safe_decode(s: Union[IO[str], AnyStr, None]) -> Optional[str]:
     """Safely decodes a binary string to unicode"""
     if isinstance(s, str):
         return s
diff --git a/git/exc.py b/git/exc.py
index c066e5e2f..358e7ae46 100644
--- a/git/exc.py
+++ b/git/exc.py
@@ -65,10 +65,12 @@ def __init__(self, command: Union[List[str], Tuple[str, ...], str],
                     status = "'%s'" % s if isinstance(status, str) else s
 
         self._cmd = safe_decode(command[0])
-        self._cmdline = ' '.join(str(safe_decode(i)) for i in command)
+        self._cmdline = ' '.join(safe_decode(i) for i in command)
         self._cause = status and " due to: %s" % status or "!"
-        self.stdout = stdout and "\n  stdout: '%s'" % safe_decode(str(stdout)) or ''
-        self.stderr = stderr and "\n  stderr: '%s'" % safe_decode(str(stderr)) or ''
+        stdout_decode = safe_decode(stdout)
+        stderr_decode = safe_decode(stderr)
+        self.stdout = stdout_decode and "\n  stdout: '%s'" % stdout_decode or ''
+        self.stderr = stderr_decode and "\n  stderr: '%s'" % stderr_decode or ''
 
     def __str__(self) -> str:
         return (self._msg + "\n  cmdline: %s%s%s") % (