diff --git a/tests/thread/stress_aes.py b/tests/thread/stress_aes.py
index 1bf252a80..ebc84d79b 100644
--- a/tests/thread/stress_aes.py
+++ b/tests/thread/stress_aes.py
@@ -267,7 +267,11 @@ def thread_entry(n_loop):
 if __name__ == "__main__":
     import sys
 
-    if sys.platform == "rp2":
+    if hasattr(sys, "settrace"):
+        # Builds with sys.settrace enabled are slow, so make the test short.
+        n_thread = 2
+        n_loop = 2
+    elif sys.platform == "rp2":
         n_thread = 1
         n_loop = 2
     elif sys.platform in ("esp32", "pyboard"):