diff --git a/.style.yapf b/.style.yapf
index 2c5517ec40..745ec88d70 100644
--- a/.style.yapf
+++ b/.style.yapf
@@ -178,3 +178,8 @@ split_penalty_logical_operator=0
 # Use the Tab character for indentation.
 use_tabs=False
 
+# Without this, yapf likes to write things like
+#   "foo bar {}".
+#   format(...)
+# which is just awful.
+split_before_dot=True
diff --git a/test-requirements.in b/test-requirements.in
index 5d63d3dc83..9f28aec952 100644
--- a/test-requirements.in
+++ b/test-requirements.in
@@ -9,7 +9,7 @@ pylint         # for pylint finding all symbols tests
 jedi           # for jedi code completion tests
 
 # Tools
-yapf == 0.22.0  # formatting; also pinned in renovate.json
+yapf == 0.24.0  # formatting
 flake8
 
 # https://github.com/python-trio/trio/pull/654#issuecomment-420518745
diff --git a/test-requirements.txt b/test-requirements.txt
index 9d226523c1..e2b1924a4b 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -47,4 +47,4 @@ trustme==0.4.0
 typed-ast==1.1.0 ; python_version < "3.7" and implementation_name == "cpython"
 wcwidth==0.1.7            # via prompt-toolkit
 wrapt==1.10.11            # via astroid
-yapf==0.22.0
+yapf==0.24.0
diff --git a/trio/_core/_run.py b/trio/_core/_run.py
index 644133bf7d..265068f96c 100644
--- a/trio/_core/_run.py
+++ b/trio/_core/_run.py
@@ -887,8 +887,9 @@ def _return_value_looks_like_wrong_library(value):
             # Give good error for: nursery.start_soon(some_sync_fn)
             raise TypeError(
                 "trio expected an async function, but {!r} appears to be "
-                "synchronous"
-                .format(getattr(async_fn, "__qualname__", async_fn))
+                "synchronous".format(
+                    getattr(async_fn, "__qualname__", async_fn)
+                )
             )
 
         ######
diff --git a/trio/_socket.py b/trio/_socket.py
index 133b32c2b9..507c4b07a6 100644
--- a/trio/_socket.py
+++ b/trio/_socket.py
@@ -389,8 +389,9 @@ def __init__(self, sock):
             # For example, ssl.SSLSocket subclasses socket.socket, but we
             # certainly don't want to blindly wrap one of those.
             raise TypeError(
-                "expected object of type 'socket.socket', not '{}"
-                .format(type(sock).__name__)
+                "expected object of type 'socket.socket', not '{}".format(
+                    type(sock).__name__
+                )
             )
         self._sock = sock
         self._sock.setblocking(False)
diff --git a/trio/_sync.py b/trio/_sync.py
index 51b095f671..f9a22b49d9 100644
--- a/trio/_sync.py
+++ b/trio/_sync.py
@@ -415,8 +415,9 @@ def __repr__(self):
         else:
             max_value_str = ", max_value={}".format(self._max_value)
         return (
-            "<trio.Semaphore({}{}) at {:#x}>"
-            .format(self._value, max_value_str, id(self))
+            "<trio.Semaphore({}{}) at {:#x}>".format(
+                self._value, max_value_str, id(self)
+            )
         )
 
     @property
@@ -524,8 +525,9 @@ def __repr__(self):
             s1 = "unlocked"
             s2 = ""
         return (
-            "<{} {} object at {:#x}{}>"
-            .format(s1, self.__class__.__name__, id(self), s2)
+            "<{} {} object at {:#x}{}>".format(
+                s1, self.__class__.__name__, id(self), s2
+            )
         )
 
     def locked(self):
@@ -858,8 +860,9 @@ def __init__(self, capacity):
 
     def __repr__(self):
         return (
-            "<Queue({}) at {:#x} holding {} items>"
-            .format(self.capacity, id(self), len(self._data))
+            "<Queue({}) at {:#x} holding {} items>".format(
+                self.capacity, id(self), len(self._data)
+            )
         )
 
     def qsize(self):
diff --git a/trio/testing/_mock_clock.py b/trio/testing/_mock_clock.py
index a013e4da79..09d3ea7091 100644
--- a/trio/testing/_mock_clock.py
+++ b/trio/testing/_mock_clock.py
@@ -100,8 +100,9 @@ def __init__(self, rate=0.0, autojump_threshold=inf):
 
     def __repr__(self):
         return (
-            "<MockClock, time={:.7f}, rate={} @ {:#x}>"
-            .format(self.current_time(), self._rate, id(self))
+            "<MockClock, time={:.7f}, rate={} @ {:#x}>".format(
+                self.current_time(), self._rate, id(self)
+            )
         )
 
     @property
diff --git a/trio/tests/test_highlevel_serve_listeners.py b/trio/tests/test_highlevel_serve_listeners.py
index c72f350618..7d237419a6 100644
--- a/trio/tests/test_highlevel_serve_listeners.py
+++ b/trio/tests/test_highlevel_serve_listeners.py
@@ -137,7 +137,8 @@ async def connection_watcher(*, task_status=trio.TASK_STATUS_IGNORED):
             await nursery.start(
                 partial(
                     trio.serve_listeners,
-                    handler, [listener],
+                    handler,
+                    [listener],
                     handler_nursery=handler_nursery
                 )
             )
diff --git a/trio/tests/test_sync.py b/trio/tests/test_sync.py
index c6842ca2f8..c30992804f 100644
--- a/trio/tests/test_sync.py
+++ b/trio/tests/test_sync.py
@@ -228,7 +228,8 @@ async def test_Semaphore_bounded():
 
 
 @pytest.mark.parametrize(
-    "lockcls", [Lock, StrictFIFOLock], ids=lambda fn: fn.__name__
+    "lockcls",
+    [Lock, StrictFIFOLock], ids=lambda fn: fn.__name__
 )
 async def test_Lock_and_StrictFIFOLock(lockcls):
     l = lockcls()  # noqa
diff --git a/trio/tests/test_testing.py b/trio/tests/test_testing.py
index 8abf8eb5ff..a7df5275d7 100644
--- a/trio/tests/test_testing.py
+++ b/trio/tests/test_testing.py
@@ -322,8 +322,9 @@ async def test_mock_clock_autojump(mock_clock):
 
     real_duration = time.monotonic() - real_start
     print(
-        "Slept {} seconds in {} seconds"
-        .format(10 * sum(range(10)), real_duration)
+        "Slept {} seconds in {} seconds".format(
+            10 * sum(range(10)), real_duration
+        )
     )
     assert real_duration < 1