diff --git a/src/lua/psl.lua b/src/lua/psl.lua
index bc2f888..ff191c9 100644
--- a/src/lua/psl.lua
+++ b/src/lua/psl.lua
@@ -81,6 +81,14 @@ end
 
 function _M.get_registered_domain(domain)
     if not domain or domain == "" then return nil end
+
+    local cache_key = "psl:" .. domain
+    local cache = ngx.shared.jasima_cache
+    local cached = cache:get(cache_key)
+    if cached then
+        return cached
+    end
+
     local rules = load_psl()
     if not rules then return nil end
 
@@ -101,7 +109,9 @@ function _M.get_registered_domain(domain)
         table.insert(reg_parts, domain_parts[i])
     end
 
-    return table.concat(reg_parts, ".")
+    local result = table.concat(reg_parts, ".")
+    cache:set(cache_key, result, 86400 * 7) -- This is very unlikely to ever change
+    return result
 end
 
 return _M