diff --git a/tests/thread_flood/Makefile b/tests/thread_flood/Makefile
index 67d8dd404..1a78b3b86 100644
--- a/tests/thread_flood/Makefile
+++ b/tests/thread_flood/Makefile
@@ -4,3 +4,8 @@ include ../Makefile.tests_common
 DISABLE_MODULE += auto_init
 
 include $(RIOTBASE)/Makefile.include
+
+test:
+# `testrunner` calls `make term` recursively, results in duplicated `TERMFLAGS`.
+# So clears `TERMFLAGS` before run.
+	TERMFLAGS= tests/test_thread.py