diff --git a/stdlib/3/subprocess.pyi b/stdlib/3/subprocess.pyi
index 80761f4e7..a64162105 100644
--- a/stdlib/3/subprocess.pyi
+++ b/stdlib/3/subprocess.pyi
@@ -46,8 +46,9 @@ if sys.version_info >= (3, 5):
                 restore_signals: bool = ...,
                 start_new_session: bool = ...,
                 pass_fds: Any = ...,
-                encoding: str = ...,
-                errors: str = ...) -> CompletedProcess: ...
+                *,
+                encoding: Optional[str] = ...,
+                errors: Optional[str] = ...) -> CompletedProcess: ...
     else:
         # Nearly same args as Popen.__init__ except for timeout, input, and check
         def run(args: _CMD,
@@ -151,7 +152,31 @@ else:
                    start_new_session: bool = ...,
                    pass_fds: Any = ...) -> int: ...
 
-if sys.version_info >= (3, 4):
+if sys.version_info >= (3, 6):
+    # 3.6 added encoding and errors
+    def check_output(args: _CMD,
+                     bufsize: int = ...,
+                     executable: _TXT = ...,
+                     stdin: _FILE = ...,
+                     stderr: _FILE = ...,
+                     preexec_fn: Callable[[], Any] = ...,
+                     close_fds: bool = ...,
+                     shell: bool = ...,
+                     cwd: _TXT = ...,
+                     env: _ENV = ...,
+                     universal_newlines: bool = ...,
+                     startupinfo: Any = ...,
+                     creationflags: int = ...,
+                     restore_signals: bool = ...,
+                     start_new_session: bool = ...,
+                     pass_fds: Any = ...,
+                     *,
+                     timeout: float = ...,
+                     input: _TXT = ...,
+                     encoding: Optional[str] = ...,
+                     errors: Optional[str] = ...,
+                     ) -> Any: ...  # morally: -> _TXT
+elif sys.version_info >= (3, 4):
     # 3.4 added input
     def check_output(args: _CMD,
                      bufsize: int = ...,
@@ -266,8 +291,9 @@ class Popen:
                      restore_signals: bool = ...,
                      start_new_session: bool = ...,
                      pass_fds: Any = ...,
-                     encoding: str = ...,
-                     errors: str = ...) -> None: ...
+                     *,
+                     encoding: Optional[str] = ...,
+                     errors: Optional[str] = ...) -> None: ...
     else:
         def __init__(self,
                      args: _CMD,