diff --git a/src/icartt/dataset.py b/src/icartt/dataset.py
index fd9cdc3beb5fa11209ed864407a1ecf20db4c6fb..5c5946ea52b48b6167d618db4c39d31e0509561a 100644
--- a/src/icartt/dataset.py
+++ b/src/icartt/dataset.py
@@ -710,10 +710,10 @@ class Dataset:
         def isAsciiAlpha(x):
             return re.match("[a-zA-Z0-9-_.]", x)
 
-        allAsciiAlpha = all([isAsciiAlpha(x) for x in name])
+        allAsciiAlpha = all(isAsciiAlpha(x) for x in name)
         lessThan128Characters = len(name) < 128
 
-        return allAsciiAlpha and lessThan128Characters
+        return allAsciiAlpha and lessThan128Characters and name.endswith('.ict')
 
     def writeHeader(self, f=sys.stdout, delimiter=DEFAULT_FIELD_DELIM):
         """Write header
@@ -914,7 +914,8 @@ class Dataset:
             else:
                 self.inputFhandle = f
 
-        # TODO should we add a filename characters check, as we have it for the variable names?
+            if not self.isValidFileName(pathlib.Path(f).name):
+                warnings.warn(f"{pathlib.Path(f).name} is not a valid ICARTT filename")
 
             self.readHeader(splitChar)
             if loadData: