diff --git a/git_command.py b/git_command.py
index 4b17f78d..2e4974fa 100644
--- a/git_command.py
+++ b/git_command.py
@@ -503,7 +503,8 @@ class GitCommand(object):
             A str containing everything read from the in_stream.
         """
         buffer = ""
-        chunk = in_stream.read1()
+        read_size = 1024 if sys.version_info < (3, 7) else -1
+        chunk = in_stream.read1(read_size)
         while chunk:
             # Convert to str.
             if not hasattr(chunk, "encode"):
@@ -513,7 +514,7 @@ class GitCommand(object):
             out_stream.write(chunk)
             out_stream.flush()
 
-            chunk = in_stream.read1()
+            chunk = in_stream.read1(read_size)
 
         return buffer