diff --git a/examples/micropython/Makefile b/examples/micropython/Makefile
index e5e7829693ef..f337823456a9 100644
--- a/examples/micropython/Makefile
+++ b/examples/micropython/Makefile
@@ -32,7 +32,7 @@ FEATURES_OPTIONAL += periph_spi
 TESTRUNNER_RESET_AFTER_TERM ?= 1
 
 # failing on native with floating point exception (#15870)
-TEST_ON_CI_BLACKLIST = native
+TEST_ON_CI_BLACKLIST += native native64
 
 # avoid running Kconfig by default
 SHOULD_RUN_KCONFIG ?=
diff --git a/tests/sys/posix_semaphore/Makefile b/tests/sys/posix_semaphore/Makefile
index 6bf4619e6ad1..5d6c34b46c46 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