diff --git a/testcases/t/234-ewmh-desktop-names.t b/testcases/t/234-ewmh-desktop-names.t
index 570e8528..d95965c4 100644
--- a/testcases/t/234-ewmh-desktop-names.t
+++ b/testcases/t/234-ewmh-desktop-names.t
@@ -20,6 +20,9 @@
 use i3test;
 
 sub get_desktop_names {
+    # Make sure that i3 pushed its changes to X11 before querying.
+    sync_with_i3;
+
     my $cookie = $x->get_property(
         0,
         $x->get_root_window(),
diff --git a/testcases/t/521-ewmh-desktop-viewport.t b/testcases/t/521-ewmh-desktop-viewport.t
index 07034cda..9e36090c 100644
--- a/testcases/t/521-ewmh-desktop-viewport.t
+++ b/testcases/t/521-ewmh-desktop-viewport.t
@@ -33,6 +33,9 @@ EOT
 my $pid = launch_with_config($config);
 
 sub get_desktop_viewport {
+    # Make sure that i3 pushed its changes to X11 before querying.
+    sync_with_i3;
+
     my $cookie = $x->get_property(
         0,
         $x->get_root_window(),