diff --git a/src/main/java/noppes/npcs/controllers/DialogController.java b/src/main/java/noppes/npcs/controllers/DialogController.java
index b9a416762..b65e1ef5e 100644
--- a/src/main/java/noppes/npcs/controllers/DialogController.java
+++ b/src/main/java/noppes/npcs/controllers/DialogController.java
@@ -84,14 +84,22 @@ public class DialogController implements IDialogHandler {
                         lastUsedDialogID = id;
                     Dialog dialog = category.dialogs.get(id);
                     if (dialogs.containsKey(id)) {
-                        // Find the next free ID, skipping any already claimed slots.
-                        int newId = lastUsedDialogID;
-                        do { newId++; } while (dialogs.containsKey(newId));
-                        lastUsedDialogID = newId;
-
                         // Dialog IDs live in the filename, not inside the JSON body,
                         // so a simple rename permanently resolves the conflict.
                         File catDir = new File(getDir(), category.title);
+
+                        // Find the next free ID. It has to clear three things: the ids already
+                        // registered globally, the ids this category still holds but has not
+                        // reached yet, and any file already on disk - renameTo overwrites
+                        // silently on POSIX, so landing on an existing file would destroy it.
+                        int newId = lastUsedDialogID;
+                        do {
+                            newId++;
+                        } while (dialogs.containsKey(newId)
+                            || category.dialogs.containsKey(newId)
+                            || new File(catDir, newId + ".json").exists());
+                        lastUsedDialogID = newId;
+
                         File oldFile = new File(catDir, id + ".json");
                         File newFile = new File(catDir, newId + ".json");
                         boolean renamed = oldFile.renameTo(newFile);
diff --git a/src/main/java/noppes/npcs/controllers/QuestController.java b/src/main/java/noppes/npcs/controllers/QuestController.java
index 69bbe88d0..3d9b707b3 100644
--- a/src/main/java/noppes/npcs/controllers/QuestController.java
+++ b/src/main/java/noppes/npcs/controllers/QuestController.java
@@ -70,6 +70,7 @@ public class QuestController implements IQuestHandler {
                 if (!file.isDirectory())
                     continue;
                 QuestCategory category = loadCategoryDir(file);
+                List<Quest> reassigned = new ArrayList<Quest>();
                 Iterator<Integer> ite = category.quests.keySet().iterator();
                 while (ite.hasNext()) {
                     int id = ite.next();
@@ -77,8 +78,39 @@ public class QuestController implements IQuestHandler {
                         lastUsedQuestID = id;
                     Quest quest = category.quests.get(id);
                     if (quests.containsKey(id)) {
-                        LogWriter.error("Duplicate id " + quest.id + " from category " + category.title);
+                        // Quest IDs live in the filename, not inside the JSON body,
+                        // so a simple rename permanently resolves the conflict.
+                        File catDir = new File(getDir(), category.title);
+
+                        // Find the next free ID. It has to clear three things: the ids already
+                        // registered globally, the ids this category still holds but has not
+                        // reached yet, and any file already on disk - renameTo overwrites
+                        // silently on POSIX, so landing on an existing file would destroy it.
+                        int newId = lastUsedQuestID;
+                        do {
+                            newId++;
+                        } while (quests.containsKey(newId)
+                            || category.quests.containsKey(newId)
+                            || new File(catDir, newId + ".json").exists());
+                        lastUsedQuestID = newId;
+
+                        File oldFile = new File(catDir, id + ".json");
+                        File newFile = new File(catDir, newId + ".json");
+                        boolean renamed = oldFile.renameTo(newFile);
+
+                        quest.id = newId;
                         ite.remove();
+                        reassigned.add(quest);
+
+                        if (renamed) {
+                            LogWriter.info("Quest ID conflict: reassigned \"" + quest.title
+                                + "\" from id " + id + " to " + newId
+                                + " in category \"" + category.title + "\"");
+                        } else {
+                            LogWriter.error("Quest ID conflict: could not rename file for \""
+                                + quest.title + "\" (id " + id
+                                + " in category \"" + category.title + "\") to " + newId);
+                        }
                     } else {
                         quests.put(id, quest);
                         if (quest.profileOptions.enableOptions
@@ -88,6 +120,16 @@ public class QuestController implements IQuestHandler {
                         }
                     }
                 }
+                // Re-register reassigned quests under their new IDs.
+                for (Quest quest : reassigned) {
+                    quests.put(quest.id, quest);
+                    category.quests.put(quest.id, quest);
+                    if (quest.profileOptions.enableOptions
+                            && (quest.profileOptions.completeControl == EnumProfileSync.Shared
+                                || quest.profileOptions.cooldownControl == EnumProfileSync.Shared)) {
+                        sharedQuests.put(quest.id, quest);
+                    }
+                }
                 lastUsedCatID++;
                 category.id = lastUsedCatID;
                 categories.put(category.id, category);