diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9af4c77bb..e52e1cbf0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,9 +2,13 @@
 
 ## PyNWB 3.1.3 (Unreleased)
 
+### Fixed
+- Fixed incorrect warning for path not ending in `.nwb` when no path argument was provided. @t-b [#2130](https://github.com/NeurodataWithoutBorders/pynwb/pull/2130)
+
 ### Documentation and tutorial enhancements
 - Change UI of assistant to be an accordion that is always visible. [#2124](https://github.com/NeurodataWithoutBorders/pynwb/pull/2124)
 
+
 ## PyNWB 3.1.2 (August 13, 2025)
 
 ### Fixed
diff --git a/src/pynwb/__init__.py b/src/pynwb/__init__.py
index c39e89e04..4a11daa86 100644
--- a/src/pynwb/__init__.py
+++ b/src/pynwb/__init__.py
@@ -428,7 +428,7 @@ def __init__(self, **kwargs):
         if mode in io_modes_that_create_file or manager is not None or extensions is not None:
             load_namespaces = False
 
-        if mode in io_modes_that_create_file and not str(path).endswith('.nwb'):
+        if mode in io_modes_that_create_file and path is not None and not str(path).endswith('.nwb'):
             warn(f"The file path provided: {path} does not end in '.nwb'. "
                  "It is recommended that NWB files using the HDF5 backend use the '.nwb' extension.", UserWarning)
 
diff --git a/tests/unit/test_file.py b/tests/unit/test_file.py
index 5338f6669..4656858fe 100644
--- a/tests/unit/test_file.py
+++ b/tests/unit/test_file.py
@@ -1,6 +1,10 @@
 import numpy as np
 import pandas as pd
 
+import h5py
+import io
+import warnings
+
 from datetime import datetime, timedelta
 from dateutil.tz import tzlocal, tzutc
 from hdmf.common import DynamicTable
@@ -711,3 +715,12 @@ class TestTimezone(TestCase):
     def test_raise_warning__add_missing_timezone(self):
         with self.assertWarnsWith(UserWarning, "Date is missing timezone information. Updating to local timezone."):
             _add_missing_timezone(datetime(2017, 5, 1, 12))
+
+class TestNoWarningWithoutPath(TestCase):
+    def test_raise_warning(self):
+        with warnings.catch_warnings():
+            warnings.simplefilter("error")
+
+            data = io.BytesIO()
+            h5file = h5py.File(data, "w")
+            NWBHDF5IO(mode = "w", file = h5file)