diff --git a/tests/pexpects/bind_mode_events.py b/tests/pexpects/bind_mode_events.py
index d7ab5d675..4bed3c1f4 100644
--- a/tests/pexpects/bind_mode_events.py
+++ b/tests/pexpects/bind_mode_events.py
@@ -44,7 +44,8 @@ expect_prompt()
 timeout = 0.15
 
 if "CI" in os.environ:
-    # This doesn't work under tsan.
+    # This doesn't work under TSan, because TSan prevents select() being
+    # interrupted by a signal.
     import sys
     print("SKIPPING the last of bind_mode_events.py")
     sys.exit(0)
diff --git a/tests/pexpects/cancel_event.py b/tests/pexpects/cancel_event.py
index c83efe857..ad6c7484c 100644
--- a/tests/pexpects/cancel_event.py
+++ b/tests/pexpects/cancel_event.py
@@ -16,7 +16,8 @@ expect_prompt()
 timeout = 0.15
 
 if "CI" in os.environ:
-    # This doesn't work under tsan.
+    # This doesn't work under TSan, because TSan prevents select() being
+    # interrupted by a signal.
     import sys
     print("SKIPPING cancel_event.py")
     sys.exit(0)