diff --git a/Spigot-Server-Patches/0335-Use-ConcurrentHashMap-in-JsonList.patch b/Spigot-Server-Patches/0335-Use-ConcurrentHashMap-in-JsonList.patch
new file mode 100644
index 000000000..e77f5399c
--- /dev/null
+++ b/Spigot-Server-Patches/0335-Use-ConcurrentHashMap-in-JsonList.patch
@@ -0,0 +1,105 @@
+From b91e3e397c77e26889b815000b9831c5fdd333c3 Mon Sep 17 00:00:00 2001
+From: egg82 <phantom_zero@ymail.com>
+Date: Tue, 7 Aug 2018 01:24:23 -0600
+Subject: [PATCH] Use ConcurrentHashMap in JsonList
+
+This is specifically aimed at fixing #471
+
+Using a ConcurrentHashMap because thread safety
+The performance benefit of Map over ConcurrentMap is negligabe at best in this scenaio, as most operations will be get and not add or remove
+Even without considering the use-case the benefits are still negligable
+
+Original ideas for the system included an expiration policy and/or handler
+The simpler solution was to use a computeIfPresent in the get method
+This will simultaneously have an O(1) lookup time and automatically expire any values
+Since the get method (nor other similar methods) don't seem to have a critical need to flush the map to disk at any of these points further processing is simply wasteful
+Meaning the original function expired values unrelated to the current value without actually having any explicit need to
+
+The h method was heavily modified to be much more efficient in its processing
+Also instead of being called on every get, it's now called just before a save
+This will eliminate stale values being flushed to disk
+
+Modified isEmpty to use the isEmpty() method instead of the slightly confusing size() < 1
+The point of this is readability, but does have a side-benefit of a small microptimization
+
+Finally, added a couple obfhelpers for the modified code
+
+diff --git a/src/main/java/net/minecraft/server/JsonList.java b/src/main/java/net/minecraft/server/JsonList.java
+index 6700e68c06..a2815b91fd 100644
+--- a/src/main/java/net/minecraft/server/JsonList.java
++++ b/src/main/java/net/minecraft/server/JsonList.java
+@@ -36,7 +36,8 @@ public class JsonList<K, V extends JsonListEntry<K>> {
+     protected static final Logger a = LogManager.getLogger();
+     protected final Gson b;
+     private final File c;
+-    private final Map<String, V> d = Maps.newHashMap();
++    // Paper - replace HashMap is ConcurrentHashMap
++    private final Map<String, V> d = Maps.newConcurrentMap(); private final Map<String, V> getBackingMap() { return this.d; } // Paper - OBFHELPER
+     private boolean e = true;
+     private static final ParameterizedType f = new ParameterizedType() {
+         public Type[] getActualTypeArguments() {
+@@ -85,8 +86,13 @@ public class JsonList<K, V extends JsonListEntry<K>> {
+ 
+     @Nullable
+     public V get(K k0) {
+-        this.h();
+-        return (V) this.d.get(this.a(k0)); // CraftBukkit - fix decompile error
++        // Paper start
++        // this.h();
++        // return (V) this.d.get(this.a(k0)); // CraftBukkit - fix decompile error
++        return (V) this.getBackingMap().computeIfPresent(this.getMappingKey(k0), (k, v) -> {
++            return v.hasExpired() ? null : v;
++        });
++        // Paper end
+     }
+ 
+     public void remove(K k0) {
+@@ -115,9 +121,11 @@ public class JsonList<K, V extends JsonListEntry<K>> {
+     // CraftBukkit end
+ 
+     public boolean isEmpty() {
+-        return this.d.size() < 1;
++        // return this.d.size() < 1; // Paper
++        return this.getBackingMap().isEmpty(); // Paper - readability is the goal. As an aside, isEmpty() uses only sumCount() and a comparison. size() uses sumCount(), casts, and boolean logic
+     }
+ 
++    protected final String getMappingKey(K k0) { return a(k0); } // Paper - OBFHELPER
+     protected String a(K k0) {
+         return k0.toString();
+     }
+@@ -126,8 +134,10 @@ public class JsonList<K, V extends JsonListEntry<K>> {
+         return this.d.containsKey(this.a(k0));
+     }
+ 
++    private void removeStaleEntries() { h(); } // Paper - OBFHELPER
+     private void h() {
+-        ArrayList arraylist = Lists.newArrayList();
++        // Paper start
++        /*ArrayList arraylist = Lists.newArrayList();
+         Iterator iterator = this.d.values().iterator();
+ 
+         while (iterator.hasNext()) {
+@@ -144,8 +154,10 @@ public class JsonList<K, V extends JsonListEntry<K>> {
+             Object object = iterator.next();
+ 
+             this.d.remove(this.a((K) object)); // CraftBukkit - decompile error
+-        }
++        }*/
+ 
++        this.getBackingMap().values().removeIf(JsonListEntry::hasExpired);
++        // Paper end
+     }
+ 
+     protected JsonListEntry<K> a(JsonObject jsonobject) {
+@@ -157,6 +169,8 @@ public class JsonList<K, V extends JsonListEntry<K>> {
+     }
+ 
+     public void save() throws IOException {
++        this.removeStaleEntries(); // Paper - remove expired values before saving
++
+         Collection collection = this.d.values();
+         String s = this.b.toJson(collection);
+         BufferedWriter bufferedwriter = null;
+-- 
+2.18.0
+