diff --git a/src/main/java/com/intellectualcrafters/plot/PS.java b/src/main/java/com/intellectualcrafters/plot/PS.java
index 13b0812da..9c19c43f0 100644
--- a/src/main/java/com/intellectualcrafters/plot/PS.java
+++ b/src/main/java/com/intellectualcrafters/plot/PS.java
@@ -193,7 +193,18 @@ public class PS {
                 @Override
                 public void run() {
                     PS.debug("Starting UUID caching");
-                    UUIDHandler.startCaching(null);
+                    UUIDHandler.startCaching(new Runnable() {
+                        @Override
+                        public void run() {
+                            for (Plot plot : getPlots()) {
+                                if (plot.owner != null && plot.temp != -1) {
+                                    if (UUIDHandler.getName(plot.owner) == null) {
+                                        UUIDHandler.implementation.unknown.add(plot.owner);
+                                    }
+                                }
+                            }
+                        }
+                    });
                 }
             }, 20);
             // create event util class
diff --git a/src/main/java/com/intellectualcrafters/plot/database/AbstractDB.java b/src/main/java/com/intellectualcrafters/plot/database/AbstractDB.java
index 88520a849..ea48bc90e 100644
--- a/src/main/java/com/intellectualcrafters/plot/database/AbstractDB.java
+++ b/src/main/java/com/intellectualcrafters/plot/database/AbstractDB.java
@@ -330,6 +330,15 @@ public interface AbstractDB {
     void resizeCluster(PlotCluster current, PlotClusterId resize);
 
     void movePlot(Plot originalPlot, Plot newPlot);
+
+    /**
+     * Replace a old uuid with a new one in the database<br>
+     * - Useful for replacing a few uuids (not the entire database)<br>
+     * - For entire conversion, the uuidconvert command scales better
+     * @param old
+     * @param now
+     */
+    void replaceUUID(UUID old, UUID now);
     
     /**
      * Don't fuck with this one, unless you enjoy it rough
diff --git a/src/main/java/com/intellectualcrafters/plot/database/DBFunc.java b/src/main/java/com/intellectualcrafters/plot/database/DBFunc.java
index fb0605f7e..1768a026e 100644
--- a/src/main/java/com/intellectualcrafters/plot/database/DBFunc.java
+++ b/src/main/java/com/intellectualcrafters/plot/database/DBFunc.java
@@ -420,6 +420,15 @@ public class DBFunc {
     public static void setPosition(final PlotCluster cluster, final String position) {
         dbManager.setPosition(cluster, position);
     }
+    
+    /**
+     * Replace all occurances of a uuid in the database with another one
+     * @param old
+     * @param now
+     */
+    public static void replaceUUID(UUID old, UUID now) {
+        dbManager.replaceUUID(old, now);
+    }
 
     public static void close() {
         dbManager.close();
diff --git a/src/main/java/com/intellectualcrafters/plot/database/SQLManager.java b/src/main/java/com/intellectualcrafters/plot/database/SQLManager.java
index 2305b9076..c4bf9192a 100644
--- a/src/main/java/com/intellectualcrafters/plot/database/SQLManager.java
+++ b/src/main/java/com/intellectualcrafters/plot/database/SQLManager.java
@@ -2572,6 +2572,28 @@ public class SQLManager implements AbstractDB {
         }
         commit();
     }
+    
+    @Override
+    public void replaceUUID(final UUID old, final UUID now) {
+        addGlobalTask(new Runnable() {
+            @Override
+            public void run() {
+                try (Statement stmt = connection.createStatement()) {
+                    stmt.executeUpdate("UPDATE `" + prefix + "cluster` SET `owner` = '" + now.toString() + "' WHERE `owner` = '" + old.toString() + "'");
+                    stmt.executeUpdate("UPDATE `" + prefix + "cluster_helpers` SET `user_uuid` = '" + now.toString() + "' WHERE `user_uuid` = '" + old.toString() + "'");
+                    stmt.executeUpdate("UPDATE `" + prefix + "cluster_invited` SET `user_uuid` = '" + now.toString() + "' WHERE `user_uuid` = '" + old.toString() + "'");
+                    stmt.executeUpdate("UPDATE `" + prefix + "plot` SET `owner` = '" + now.toString() + "' WHERE `owner` = '" + old.toString() + "'");
+                    stmt.executeUpdate("UPDATE `" + prefix + "plot_denied` SET `user_uuid` = '" + now.toString() + "' WHERE `user_uuid` = '" + old.toString() + "'");
+                    stmt.executeUpdate("UPDATE `" + prefix + "plot_helpers` SET `user_uuid` = '" + now.toString() + "' WHERE `user_uuid` = '" + old.toString() + "'");
+                    stmt.executeUpdate("UPDATE `" + prefix + "plot_trusted` SET `user_uuid` = '" + now.toString() + "' WHERE `user_uuid` = '" + old.toString() + "'");
+                    stmt.close();
+                }
+                catch (Exception e) {
+                    e.printStackTrace();
+                }
+            }
+        });
+    }
 
     @Override
     public void close() {
diff --git a/src/main/java/com/intellectualcrafters/plot/util/UUIDHandlerImplementation.java b/src/main/java/com/intellectualcrafters/plot/util/UUIDHandlerImplementation.java
index 70986f50c..3deb4f649 100644
--- a/src/main/java/com/intellectualcrafters/plot/util/UUIDHandlerImplementation.java
+++ b/src/main/java/com/intellectualcrafters/plot/util/UUIDHandlerImplementation.java
@@ -1,15 +1,20 @@
 package com.intellectualcrafters.plot.util;
 
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.Map;
+import java.util.Set;
 import java.util.UUID;
 
+import com.google.common.base.Charsets;
 import com.google.common.collect.BiMap;
 import com.google.common.collect.HashBiMap;
 import com.intellectualcrafters.plot.PS;
 import com.intellectualcrafters.plot.config.C;
 import com.intellectualcrafters.plot.config.Settings;
+import com.intellectualcrafters.plot.database.DBFunc;
 import com.intellectualcrafters.plot.object.OfflinePlotPlayer;
+import com.intellectualcrafters.plot.object.Plot;
 import com.intellectualcrafters.plot.object.PlotPlayer;
 import com.intellectualcrafters.plot.object.RunnableVal;
 import com.intellectualcrafters.plot.object.StringWrapper;
@@ -62,36 +67,82 @@ public abstract class UUIDHandlerImplementation {
         if (uuidMap.size() == 0) {
             uuidMap = toAdd;
         }
-        TaskManager.runTask(new Runnable() {
-            @Override
-            public void run() {
-                for (Map.Entry<StringWrapper, UUID> entry : toAdd.entrySet()) {
-                    UUID uuid = entry.getValue();
-                    StringWrapper name = entry.getKey();
-                    if ((uuid == null) || (name == null)) {
-                        continue;
-                    }
-                    BiMap<UUID, StringWrapper> inverse = uuidMap.inverse();
-                    if (inverse.containsKey(uuid)) {
-                        if (uuidMap.containsKey(name)) {
-                            continue;
-                        }
-                        rename(uuid, name);
-                        continue;
-                    }
-                    uuidMap.put(name, uuid);
-                }
-                PS.debug(C.PREFIX.s() + "&6Cached a total of: " + uuidMap.size() + " UUIDs");
+        for (Map.Entry<StringWrapper, UUID> entry : toAdd.entrySet()) {
+            UUID uuid = entry.getValue();
+            StringWrapper name = entry.getKey();
+            if ((uuid == null) || (name == null)) {
+                continue;
             }
-        });
+            BiMap<UUID, StringWrapper> inverse = uuidMap.inverse();
+            if (inverse.containsKey(uuid)) {
+                if (uuidMap.containsKey(name)) {
+                    continue;
+                }
+                rename(uuid, name);
+                continue;
+            }
+            uuidMap.put(name, uuid);
+        }
+        PS.debug(C.PREFIX.s() + "&6Cached a total of: " + uuidMap.size() + " UUIDs");
     }
     
+    public HashSet<UUID> unknown = new HashSet<>();
+    
     public boolean add(final StringWrapper name, final UUID uuid) {
-        if ((uuid == null) || (name == null)) {
+        if ((uuid == null)) {
             return false;
         }
+        if (name == null) {
+            try {
+                unknown.add(uuid);
+            }
+            catch (Exception e) {
+                PS.log("&c(minor) Invalid UUID mapping: " + uuid);
+                e.printStackTrace();
+            }
+            return false;
+        }
+        
+        /*
+         * lazy UUID conversion:
+         *  - Useful if the person misconfigured the database, or settings before PlotMe conversion
+         */
+        if (!Settings.OFFLINE_MODE) {
+            UUID offline = UUID.nameUUIDFromBytes(("OfflinePlayer:" + name.value).getBytes(Charsets.UTF_8));
+            if (!unknown.contains(offline) && !name.value.equals(name.value.toLowerCase())){
+                offline = UUID.nameUUIDFromBytes(("OfflinePlayer:" + name.value).getBytes(Charsets.UTF_8));
+                if (!unknown.contains(offline)) {
+                    offline = null;
+                }
+            }
+            if (offline != null) {
+                unknown.remove(offline);
+                Set<Plot> plots = PS.get().getPlots(offline);
+                if (plots.size() > 0) {
+                    for (Plot plot : PS.get().getPlots(offline)) {
+                        plot.owner = uuid;
+                    }
+                    DBFunc.replaceUUID(offline, uuid);
+                    PS.debug("&cDetected invalid UUID stored for: " + name.value);
+                    PS.debug("&7 - Did you recently switch to online-mode storage without running `uuidconvert`?");
+                    PS.debug("&6PlotSquared will update incorrect entries when the user logs in, or you can reconstruct your database.");
+                }
+            }
+        }
         try {
-            uuidMap.put(name, uuid);
+            UUID offline = uuidMap.put(name, uuid);
+            if (offline != null && !offline.equals(uuid)) {
+                Set<Plot> plots = PS.get().getPlots(offline);
+                if (plots.size() > 0) {
+                    for (Plot plot : PS.get().getPlots(offline)) {
+                        plot.owner = uuid;
+                    }
+                    DBFunc.replaceUUID(offline, uuid);
+                    PS.debug("&cDetected invalid UUID stored for (1): " + name.value);
+                    PS.debug("&7 - Did you recently switch to online-mode storage without running `uuidconvert`?");
+                    PS.debug("&6PlotSquared will update incorrect entries when the user logs in, or you can reconstruct your database.");
+                }
+            }
         }
         catch (Exception e) {
             BiMap<UUID, StringWrapper> inverse = uuidMap.inverse();
diff --git a/target/PlotSquared-Bukkit.jar b/target/PlotSquared-Bukkit.jar
index d9a41481e..b0e1b072c 100644
Binary files a/target/PlotSquared-Bukkit.jar and b/target/PlotSquared-Bukkit.jar differ
diff --git a/target/PlotSquared-Sponge.jar b/target/PlotSquared-Sponge.jar
index 2ba5f269f..6356c96ff 100644
Binary files a/target/PlotSquared-Sponge.jar and b/target/PlotSquared-Sponge.jar differ