diff --git a/tests/run.sh b/tests/run.sh
index 592b7646..f2902f8f 100755
--- a/tests/run.sh
+++ b/tests/run.sh
@@ -185,6 +185,20 @@ fi
 start_awesome() {
     cd "$build_dir"
 
+    # On some systems clients from a test may still linger for a while until they
+    # are fully killed. Since this can affect susequent tests, we wait until all
+    # of them are gone.
+    # The check command needs to call `xlsclients` twice:
+    # 1. Test the stdout of `xlsclients` and make sure there are no clients left.
+    # 2. Check and fail if `xlsclients` itself fails. Print its stderr, if any.
+    # This is due to the fact that, if `xlsclient` return non-0, the `wc` would
+    # still report `0`. The order of commands makes sure that `xlsclient` is only
+    # called twice when needed. If there are still clients left, the `[` will
+    # shotcurcuit.
+    wait_until_success \
+        'wait for X clients from previous test to close' \
+        "[ \$(DISPLAY="$D" xlsclients | wc -l) -eq 0 ] && DISPLAY="$D" xlsclients > /dev/null"
+
     # Kill awesome after $TEST_TIMEOUT seconds (e.g. for errors during test setup).
     # SOURCE_DIRECTORY is used by .luacov.
     DISPLAY="$D" SOURCE_DIRECTORY="$source_dir" \
diff --git a/tests/test-leak-client.lua b/tests/test-leak-client.lua
index 12b520e4..9f326750 100644
--- a/tests/test-leak-client.lua
+++ b/tests/test-leak-client.lua
@@ -85,12 +85,25 @@ local steps = {
             -- Test that we have a client and that it's invalid (tostring()
             -- causes an "invalid object" error)
             local success, msg = pcall(function() tostring(objs[1]) end)
-            assert(not success)
+            assert(not success, msg)
             assert(msg:find("invalid object"), msg)
 
             -- Check that it is garbage-collectable
             collectgarbage("collect")
-            assert(#objs == 0)
+
+            -- On GitHub Actions, it can take a while for clients to be killed
+            -- properly.
+            local tries = 0
+            while (#objs > 0 and tries < 60) do
+                os.execute("sleep 1")
+                tries = tries + 1
+            end
+
+            if tries > 0 then
+                print("Took approx. " .. tries .. " seconds to clean leaked client")
+            end
+
+            assert(#objs == 0, "still clients left after garbage collect")
             return true
         end
     end,