diff --git a/src/ptvsd/adapter/ide.py b/src/ptvsd/adapter/ide.py
index 7f516bbd..bbf50c3e 100644
--- a/src/ptvsd/adapter/ide.py
+++ b/src/ptvsd/adapter/ide.py
@@ -304,13 +304,18 @@ class IDE(components.Component, sockets.ClientConnection):
         # will be the one for the root debuggee process, but if it has exited already,
         # it will be some subprocess.
 
-        pid = request("processId", int, optional=True)
+        pid = request("processId", (int, unicode), optional=True)
         sub_pid = request("subProcessId", int, optional=True)
         if pid != ():
             if sub_pid != ():
                 raise request.isnt_valid(
                     '"processId" and "subProcessId" are mutually exclusive'
                 )
+            if not isinstance(pid, int):
+                try:
+                    pid = int(pid)
+                except Exception:
+                    raise request.isnt_valid('"processId" must be parseable as int')
             ptvsd_args = request("ptvsdArgs", json.array(unicode))
             servers.inject(pid, ptvsd_args)
             timeout = 10
diff --git a/tests/debug/session.py b/tests/debug/session.py
index 5f18af83..03926dd4 100644
--- a/tests/debug/session.py
+++ b/tests/debug/session.py
@@ -142,6 +142,11 @@ class Session(object):
         )
         """The debug configuration for this session."""
 
+        self.before_request = lambda command, arguments: None
+        """Invoked for every outgoing request in this session, allowing any final
+        tweaks to the request before it is sent.
+        """
+
         self.log_dir = (
             None
             if log.log_dir is None
@@ -437,6 +442,8 @@ class Session(object):
         )
 
     def send_request(self, command, arguments=None, proceed=True):
+        self.before_request(command, arguments)
+
         if self.timeline.is_frozen and proceed:
             self.proceed()
 
diff --git a/tests/ptvsd/server/test_attach.py b/tests/ptvsd/server/test_attach.py
index 636fc285..50037697 100644
--- a/tests/ptvsd/server/test_attach.py
+++ b/tests/ptvsd/server/test_attach.py
@@ -130,7 +130,8 @@ def test_reattach(pyfile, target, run):
         session2.request_continue()
 
 
-def test_attach_by_pid(pyfile, target):
+@pytest.mark.parametrize("pid_type", ["int", "str"])
+def test_attach_by_pid(pyfile, target, pid_type):
     @pyfile
     def code_to_debug():
         import debug_me  # noqa
@@ -147,6 +148,13 @@ def test_attach_by_pid(pyfile, target):
                 break
 
     with debug.Session() as session:
+        def before_request(command, arguments):
+            if command == "attach":
+                assert isinstance(arguments["processId"], int)
+                if pid_type == "str":
+                    arguments["processId"] = str(arguments["processId"])
+
+        session.before_request = before_request
         session.config["redirectOutput"] = True
 
         with session.attach_by_pid(target(code_to_debug), wait=False):