diff --git a/core/src/main/java/ch/dissem/bitmessage/utils/TTL.java b/core/src/main/java/ch/dissem/bitmessage/utils/TTL.java
index 17e31e5..d1feb8a 100644
--- a/core/src/main/java/ch/dissem/bitmessage/utils/TTL.java
+++ b/core/src/main/java/ch/dissem/bitmessage/utils/TTL.java
@@ -3,9 +3,8 @@ package ch.dissem.bitmessage.utils;
 import static ch.dissem.bitmessage.utils.UnixTime.DAY;
 
 /**
- * Stores times to live for different object types. Usually this shouldn't be messed with,
- * but for tests it might be a good idea to reduce it to a minimum, and on mobile clients
- * you might want to optimize it as well.
+ * Stores times to live in seconds for different object types. Usually this shouldn't be messed with, but for tests
+ * it might be a good idea to reduce it to a minimum, and on mobile clients you might want to optimize it as well.
  *
  * @author Christian Basler
  */
@@ -19,7 +18,7 @@ public class TTL {
     }
 
     public static void msg(long msg) {
-        TTL.msg = msg;
+        TTL.msg = validate(msg);
     }
 
     public static long getpubkey() {
@@ -27,7 +26,7 @@ public class TTL {
     }
 
     public static void getpubkey(long getpubkey) {
-        TTL.getpubkey = getpubkey;
+        TTL.getpubkey = validate(getpubkey);
     }
 
     public static long pubkey() {
@@ -35,6 +34,11 @@ public class TTL {
     }
 
     public static void pubkey(long pubkey) {
-        TTL.pubkey = pubkey;
+        TTL.pubkey = validate(pubkey);
+    }
+
+    private static long validate(long ttl) {
+        if (ttl < 0 || ttl > 28 * DAY) throw new IllegalArgumentException("TTL must be between 1 and 28 days");
+        return ttl;
     }
 }