diff --git a/docs/changelog.rst b/docs/changelog.rst
index dfbf1643..92cd8966 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -21,6 +21,7 @@ To avail of fixes in an unreleased version, please download a ZIP file
 In progress (unreleased)
 ------------------------
 
+* :gh:issue:`1121` :mod:`mitogen`: Log skipped :py:mod:`termios` attributes
 
 
 v0.3.22 (2025-02-04)
diff --git a/mitogen/parent.py b/mitogen/parent.py
index 3c5e48ba..5b397d9f 100644
--- a/mitogen/parent.py
+++ b/mitogen/parent.py
@@ -224,8 +224,16 @@ def flags(names):
     Return the result of ORing a set of (space separated) :py:mod:`termios`
     module constants together.
     """
-    return sum(getattr(termios, name, 0)
-               for name in names.split())
+    i = 0
+    skipped = []
+    for name in names.split():
+        try:
+            i |= getattr(termios, name)
+        except AttributeError:
+            skipped.append(name)
+    if skipped:
+        LOG.debug('Skipped termios attributes: %s', ', '.join(skipped))
+    return i
 
 
 def cfmakeraw(tflags):