diff --git a/git/cmd.py b/git/cmd.py
index b6305176b..081edf082 100644
--- a/git/cmd.py
+++ b/git/cmd.py
@@ -78,17 +78,19 @@ def handle_process_output(process, stdout_handler, stderr_handler,
         Set it to False if `universal_newline == True` (then streams are in text-mode)
         or if decoding must happen later (i.e. for Diffs).
     """
+    pumped_lines = {'stdout': [], 'stderr': []}
     # Use 2 "pupm" threads and wait for both to finish.
     def pump_stream(cmdline, name, stream, is_decode, handler):
         try:
             for line in stream:
+                if is_decode:
+                    line = line.decode(defenc)
+                pumped_lines[name].append(line)
                 if handler:
-                    if is_decode:
-                        line = line.decode(defenc)
                     handler(line)
         except Exception as ex:
             log.error("Pumping %r of cmd(%s) failed due to: %r", name, cmdline, ex)
-            raise CommandError(['<%s-pump>' % name] + cmdline, ex)
+            raise CommandError(['<%s-pump>' % name] + cmdline, ex, **pumped_lines)
         finally:
             stream.close()
 
@@ -104,20 +106,29 @@ def pump_stream(cmdline, name, stream, is_decode, handler):
 
     threads = []
 
-    for name, stream, handler in pumps:
-        t = threading.Thread(target=pump_stream,
-                             args=(cmdline, name, stream, decode_streams, handler))
-        t.setDaemon(True)
-        t.start()
-        threads.append(t)
+    try:
+        for name, stream, handler in pumps:
+            t = threading.Thread(target=pump_stream,
+                                 args=(cmdline, name, stream, decode_streams, handler))
+            t.setDaemon(True)
+            t.start()
+            threads.append(t)
+
+        ## FIXME: Why Join??  Will block if `stdin` needs feeding...
+        #
+        for t in threads:
+            t.join()
+
+        if finalizer:
+            return finalizer(process)
+    except Exception as e:
+        for outname, out in pumped_lines.items():
+            if out and hasattr(e, outname):
+                eout = getattr(e, outname)
+                if not eout:
+                    setattr(e, outname, safe_decode(os.linesep.join(out)))
+        raise
 
-    ## FIXME: Why Join??  Will block if `stdin` needs feeding...
-    #
-    for t in threads:
-        t.join()
-
-    if finalizer:
-        return finalizer(process)
 
 
 def dashify(string):
diff --git a/git/exc.py b/git/exc.py
index 4865da944..4f5ef7b2c 100644
--- a/git/exc.py
+++ b/git/exc.py
@@ -55,12 +55,16 @@ def __init__(self, command, status=None, stderr=None, stdout=None):
         self._cmd = safe_decode(command[0])
         self._cmdline = u' '.join(safe_decode(i) for i in command)
         self._cause = status and u" due to: %s" % status or "!"
-        self.stdout = stdout and u"\n  stdout: '%s'" % safe_decode(stdout) or ''
-        self.stderr = stderr and u"\n  stderr: '%s'" % safe_decode(stderr) or ''
+        self.stdout = stdout and safe_decode(stdout) or ''
+        self.stderr = stderr and safe_decode(stderr) or ''
 
     def __unicode__(self):
         return (self._msg + "\n  cmdline: %s%s%s") % (
-            self._cmd, self._cause, self._cmdline, self.stdout, self.stderr)
+            self._cmd, self._cause,
+            self._cmdline,
+            u"\n  stdout: '%s'" % self.stdout if self.stdout else '',
+            u"\n  stderr: '%s'" % self.stderr if self.stderr else ''
+        )
 
 
 class GitCommandNotFound(CommandError):