diff --git a/requirements-dev.lock b/requirements-dev.lock
index e5e63ed037..a47de9656a 100644
--- a/requirements-dev.lock
+++ b/requirements-dev.lock
@@ -83,7 +83,7 @@ msal==1.29.0
     # via msal-extensions
 msal-extensions==1.2.0
     # via azure-identity
-mypy==1.7.1
+mypy==1.11.2
 mypy-extensions==1.0.0
     # via black
     # via mypy
@@ -125,7 +125,7 @@ pygments==2.18.0
     # via rich
 pyjwt==2.8.0
     # via msal
-pyright==1.1.374
+pyright==1.1.380
 pytest==7.1.1
     # via pytest-asyncio
 pytest-asyncio==0.21.1
diff --git a/src/openai/_utils/_utils.py b/src/openai/_utils/_utils.py
index 2fc5a1c65a..0bba17caad 100644
--- a/src/openai/_utils/_utils.py
+++ b/src/openai/_utils/_utils.py
@@ -363,12 +363,13 @@ def file_from_path(path: str) -> FileTypes:
 
 def get_required_header(headers: HeadersLike, header: str) -> str:
     lower_header = header.lower()
-    if isinstance(headers, Mapping):
-        for k, v in headers.items():
+    if is_mapping_t(headers):
+        # mypy doesn't understand the type narrowing here
+        for k, v in headers.items():  # type: ignore
             if k.lower() == lower_header and isinstance(v, str):
                 return v
 
-    """ to deal with the case where the header looks like Stainless-Event-Id """
+    # to deal with the case where the header looks like Stainless-Event-Id
     intercaps_header = re.sub(r"([^\w])(\w)", lambda pat: pat.group(1) + pat.group(2).upper(), header.capitalize())
 
     for normalized_header in [header, lower_header, header.upper(), intercaps_header]: