diff --git a/httpcore/_async/http2.py b/httpcore/_async/http2.py
index d7412f0f..c832d1e7 100644
--- a/httpcore/_async/http2.py
+++ b/httpcore/_async/http2.py
@@ -23,10 +23,8 @@
 
 def has_body_headers(request: Request) -> bool:
     return any(
-        [
-            k.lower() == b"content-length" or k.lower() == b"transfer-encoding"
-            for k, v in request.headers
-        ]
+        k.lower() == b"content-length" or k.lower() == b"transfer-encoding"
+        for k, v in request.headers
     )
 
 
diff --git a/httpcore/_async/http_proxy.py b/httpcore/_async/http_proxy.py
index 48d37cd3..b69430fc 100644
--- a/httpcore/_async/http_proxy.py
+++ b/httpcore/_async/http_proxy.py
@@ -35,7 +35,7 @@ def merge_headers(
     """
     default_headers = [] if default_headers is None else list(default_headers)
     override_headers = [] if override_headers is None else list(override_headers)
-    has_override = set([key.lower() for key, value in override_headers])
+    has_override = set(key.lower() for key, value in override_headers)
     default_headers = [
         (key, value)
         for key, value in default_headers
diff --git a/httpcore/_models.py b/httpcore/_models.py
index c9781959..bc557606 100644
--- a/httpcore/_models.py
+++ b/httpcore/_models.py
@@ -117,7 +117,7 @@ def include_request_headers(
     url: "URL",
     content: Union[None, bytes, Iterable[bytes], AsyncIterable[bytes]],
 ) -> List[Tuple[bytes, bytes]]:
-    headers_set = set([k.lower() for k, v in headers])
+    headers_set = set(k.lower() for k, v in headers)
 
     if b"host" not in headers_set:
         default_port = DEFAULT_PORTS.get(url.scheme)
diff --git a/httpcore/_sync/http2.py b/httpcore/_sync/http2.py
index 7fd29a5a..a0244bbb 100644
--- a/httpcore/_sync/http2.py
+++ b/httpcore/_sync/http2.py
@@ -23,10 +23,8 @@
 
 def has_body_headers(request: Request) -> bool:
     return any(
-        [
-            k.lower() == b"content-length" or k.lower() == b"transfer-encoding"
-            for k, v in request.headers
-        ]
+        k.lower() == b"content-length" or k.lower() == b"transfer-encoding"
+        for k, v in request.headers
     )
 
 
diff --git a/httpcore/_sync/http_proxy.py b/httpcore/_sync/http_proxy.py
index 3dadf9af..c70d8c9c 100644
--- a/httpcore/_sync/http_proxy.py
+++ b/httpcore/_sync/http_proxy.py
@@ -35,7 +35,7 @@ def merge_headers(
     """
     default_headers = [] if default_headers is None else list(default_headers)
     override_headers = [] if override_headers is None else list(override_headers)
-    has_override = set([key.lower() for key, value in override_headers])
+    has_override = set(key.lower() for key, value in override_headers)
     default_headers = [
         (key, value)
         for key, value in default_headers