diff --git a/simutrans/ai/sqai_rail/ai.nut b/simutrans/ai/sqai_rail/ai.nut
index d9e0ab7fce6..dd1c1789a77 100644
--- a/simutrans/ai/sqai_rail/ai.nut
+++ b/simutrans/ai/sqai_rail/ai.nut
@@ -321,9 +321,13 @@ function today_plus_months(m)
 function get_set_name()
 {
   local pakset = get_pakset_name()  // full string from ground.outside.pak
-  local s = pakset.find(" ")
-  pakset = pakset.slice(0, s)
-  pakset = pakset.tolower()
+  if ( pakset != null ) {
+    local s = pakset.find(" ")
+    pakset = pakset.slice(0, s)
+    pakset = pakset.tolower()
+  } else {
+    pakset = "unknown"
+  }
 
   return pakset
 }