diff --git a/lib/Properties.hs b/lib/Properties.hs
index 18a05200279b9931f4913795eca23ab682c3e61e..291827f11cb1532992b4f7a6bd1c37f7764b8e27 100644
--- a/lib/Properties.hs
+++ b/lib/Properties.hs
@@ -363,7 +363,7 @@ checkTileThing removeExits p@(Property name _value) = case name of
         suggestProperty $ Property "jitsiTrigger" "onaction"
 
         -- prevents namespace clashes for jitsi room names
-        if "shared" `isPrefixOf` jitsiRoom then do
+        if not ("shared" `isPrefixOf` jitsiRoom) then do
           assemblyname <- lintConfig configAssemblyTag
           setProperty "jitsiRoom" (assemblyname <> "-" <> jitsiRoom)
           offersJitsi (assemblyname <> "-" <> jitsiRoom)