diff --git a/tests/sys/posix_semaphore/Makefile b/tests/sys/posix_semaphore/Makefile
index 6bf4619e6a..5d6c34b46c 100644
--- a/tests/sys/posix_semaphore/Makefile
+++ b/tests/sys/posix_semaphore/Makefile
@@ -7,4 +7,8 @@ USEMODULE += ztimer64_usec
 # microbit qemu failing currently
 TEST_ON_CI_BLACKLIST += microbit
 
+# native / native64 may fail under load with:
+#    first: waited too long <NUM> usec => FAILED
+TEST_ON_CI_BLACKLIST += native native64
+
 include $(RIOTBASE)/Makefile.include