diff --git a/tests/functional/flow-triggers/11-wait-merge.t b/tests/functional/flow-triggers/11-wait-merge.t
index d869cc19600..053b768d724 100644
--- a/tests/functional/flow-triggers/11-wait-merge.t
+++ b/tests/functional/flow-triggers/11-wait-merge.t
@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 # THIS FILE IS PART OF THE CYLC WORKFLOW ENGINE.
 # Copyright (C) NIWA & British Crown (Met Office) & Contributors.
-# 
+#
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
 # the Free Software Foundation, either version 3 of the License, or
@@ -17,6 +17,7 @@
 #-------------------------------------------------------------------------------
 
 . "$(dirname "$0")/test_header"
+skip_macos_gh_actions
 set_test_number 4
 
 install_and_validate "${TEST_NAME_BASE}" "${TEST_NAME_BASE}" true
diff --git a/tests/functional/lib/bash/test_header b/tests/functional/lib/bash/test_header
index cc0f6e0af43..016b77635f0 100644
--- a/tests/functional/lib/bash/test_header
+++ b/tests/functional/lib/bash/test_header
@@ -782,6 +782,13 @@ skip_all() {
     exit
 }
 
+skip_macos_gh_actions() {
+    # https://github.com/cylc/cylc-flow/issues/6276
+    if [[ "$CI" && "$OSTYPE" == "darwin"* ]]; then
+        skip_all "Skipped due to performance issues on GH Actions MacOS runner"
+    fi
+}
+
 ssh_install_cylc() {
     local RHOST="$1"
     local RHOST_CYLC_DIR=
diff --git a/tests/functional/modes/04-simulation-runtime.t b/tests/functional/modes/04-simulation-runtime.t
index 1ce3850f202..f702680274c 100644
--- a/tests/functional/modes/04-simulation-runtime.t
+++ b/tests/functional/modes/04-simulation-runtime.t
@@ -18,6 +18,7 @@
 # Test that we can broadcast an alteration to simulation mode.
 
 . "$(dirname "$0")/test_header"
+skip_macos_gh_actions
 set_test_number 7
 
 install_workflow "${TEST_NAME_BASE}" "${TEST_NAME_BASE}"