diff --git a/tests/test_posixtest.py b/tests/test_posixtest.py
index 63d04d350a185..1820eb3f9912b 100644
--- a/tests/test_posixtest.py
+++ b/tests/test_posixtest.py
@@ -135,9 +135,16 @@ def get_pthread_tests():
   'test_pthread_spin_lock_3_1': 'signals are not supported',
 }
 
+# Mark certain tests as flaky, which may sometimes fail.
+# TODO invesigate these tests.
+flaky = {
+  'test_pthread_cond_signal_1_1': 'flaky: https://github.com/emscripten-core/emscripten/issues/13283',
+}
+
 # Mark certain tests as not passing
 disabled = {
   **unsupported,
+  **flaky,
   'test_pthread_create_11_1': 'never returns',
   'test_pthread_barrier_wait_2_1': 'never returns',
   'test_pthread_cond_timedwait_2_6': 'never returns',