diff --git a/neo/rawio/neuralynxrawio/nlxheader.py b/neo/rawio/neuralynxrawio/nlxheader.py
index 54bd57c99..292ed8458 100644
--- a/neo/rawio/neuralynxrawio/nlxheader.py
+++ b/neo/rawio/neuralynxrawio/nlxheader.py
@@ -1,6 +1,7 @@
 from packaging.version import Version
 import os
 import re
+import warnings
 from collections import OrderedDict
 
 from neo.rawio.neuralynxrawio.ncssections import AcqType
@@ -350,7 +351,11 @@ def _setTimeDate(self, txt_header):
             sr = NlxHeader._closeDatetime2_pat.search(txt_header)
         if sr:
             dt2 = sr.groupdict()
-            self["recording_closed"] = dateutil.parser.parse(f"{dt2['date']} {dt2['time']}")
+            if (dt2["date"], dt2["time"]) == ("File", "was"):
+                # Cheetah writes this in place of the close time, see #1901
+                warnings.warn("Text header does not contain recording closed time. File was not closed properly.")
+            else:
+                self["recording_closed"] = dateutil.parser.parse(f"{dt2['date']} {dt2['time']}")
 
     def _normalize_types(self):
         """
diff --git a/neo/test/rawiotest/test_neuralynxrawio.py b/neo/test/rawiotest/test_neuralynxrawio.py
index 0a1c90980..4f2581e1d 100644
--- a/neo/test/rawiotest/test_neuralynxrawio.py
+++ b/neo/test/rawiotest/test_neuralynxrawio.py
@@ -563,5 +563,17 @@ def test_filename_prop(self):
         self.assertEqual(r"C:\CheetahData\2000-01-01_00-00-00\CSC5.ncs", hdr["OriginalFileName"])
 
 
+class TestNlxHeaderParsing(unittest.TestCase):
+    def test_unclosed_recording(self):
+        header = NlxHeader.__new__(NlxHeader)
+        with self.assertWarnsRegex(UserWarning, "File was not closed properly"):
+            header._setTimeDate(
+                "## Time Opened: (m/d/y): 1/1/2000 (h:m:s.ms) 18:28:39.821\n"
+                "## Date Closed: (m/d/y): File At Time: was not properly closed"
+            )
+
+        self.assertIsNone(header.get("recording_closed"))
+
+
 if __name__ == "__main__":
     unittest.main()