diff --git a/apps/dns_proxy/src/dns_cache.erl b/apps/dns_proxy/src/dns_cache.erl
index 86d20d4..a46f3b4 100644
--- a/apps/dns_proxy/src/dns_cache.erl
+++ b/apps/dns_proxy/src/dns_cache.erl
@@ -29,20 +29,33 @@ lookup(#dns_query{name = Qname, type = QType, class = QClass}) ->
 
 insert(#dns_query{name = Qname, type = QType, class = QClass},
     #dns_message{answers = Answers, authority = Authority, additional = Additional, aa = AA}) ->
+    TTLs = lists:foldl(fun(Term, Acc) ->
+        case Term of
+            #dns_rr{ttl = TTL} ->
+                [TTL|Acc];
+            _ ->
+                Acc
+        end
+                       end, [], Answers ++ Authority ++ Additional),
+    case length(TTLs) > 0 of
+        true ->
+            TTL = lists:min(TTLs),
+            ExpireAt = os:system_time(second) + TTL,
 
-    TTLs = [RR#dns_rr.ttl || RR <- Answers] ++ [RR#dns_rr.ttl || RR <- Authority] ++ [RR#dns_rr.ttl || RR <- Additional],
-    TTL = lists:min(TTLs),
-    ExpireAt = os:system_time(second) + TTL,
+            lager:debug("min ttl is: ~p, expire_at: ~p", [TTL, ExpireAt]),
 
-    Key = {Qname, QType, QClass},
-    Cache = #dns_cache{
-        key = Key,
-        answers = Answers,
-        authority  = Authority,
-        additional = Additional,
-        rcode = 0,
-        flags = #{aa => AA},
-        % unix time
-        expire_at = ExpireAt
-    },
-    true = ets:insert(?TABLE, Cache).
+            Key = {Qname, QType, QClass},
+            Cache = #dns_cache{
+                key = Key,
+                answers = Answers,
+                authority  = Authority,
+                additional = Additional,
+                rcode = 0,
+                flags = #{aa => AA},
+                % unix time
+                expire_at = ExpireAt
+            },
+            true = ets:insert(?TABLE, Cache);
+        false ->
+            ok
+    end.
\ No newline at end of file