diff --git a/src/diagnostics.lua b/src/diagnostics.lua
index f399a76..3b11798 100644
--- a/src/diagnostics.lua
+++ b/src/diagnostics.lua
@@ -144,12 +144,13 @@ function M.validate_diagnostics(content, workspace_types, root_dir)
           type_part = type_part:gsub("%s*$", "")
           type_part = type_part:gsub("^%s+", "")
 
-          local base_type = type_part:match("^([%w_]+)")
+          -- Handle quoted type names like "MyUDT"
+          local base_type = type_part:match('^"([^"]+)"') or type_part:match("^([%w_]+)")
           if type_part:match("%s+OF%s+") then
-            base_type = type_part:match(".*%s+OF%s+([%w_]+)")
+            base_type = type_part:match('.*%s+OF%s+"([^"]+)"') or type_part:match(".*%s+OF%s+([%w_]+)")
           end
           local upper_type = base_type and base_type:upper() or nil
-          if base_type and not all_types[base_type] and
+          if base_type and base_type ~= "" and not all_types[base_type] and
              upper_type ~= "BOOL" and upper_type ~= "INT" and upper_type ~= "DINT" and
              upper_type ~= "REAL" and upper_type ~= "LREAL" and upper_type ~= "BYTE" and
              upper_type ~= "WORD" and upper_type ~= "DWORD" and upper_type ~= "LWORD" and