diff --git a/src/main/java/org/bukkit/craftbukkit/CraftServer.java b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
index a793b8f7cb..3c1f3f5315 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
@@ -398,10 +398,10 @@ public final class CraftServer implements Server {
             return found;
         }
 
-        String lowerName = name.toLowerCase();
+        String lowerName = name.toLowerCase(java.util.Locale.ENGLISH);
         int delta = Integer.MAX_VALUE;
         for (Player player : getOnlinePlayers()) {
-            if (player.getName().toLowerCase().startsWith(lowerName)) {
+            if (player.getName().toLowerCase(java.util.Locale.ENGLISH).startsWith(lowerName)) {
                 int curDelta = Math.abs(player.getName().length() - lowerName.length());
                 if (curDelta < delta) {
                     found = player;
@@ -458,7 +458,7 @@ public final class CraftServer implements Server {
                 matchedPlayers.add(iterPlayer);
                 break;
             }
-            if (iterPlayerName.toLowerCase().contains(partialName.toLowerCase())) {
+            if (iterPlayerName.toLowerCase(java.util.Locale.ENGLISH).contains(partialName.toLowerCase(java.util.Locale.ENGLISH))) {
                 // Partial match
                 matchedPlayers.add(iterPlayer);
             }
@@ -872,7 +872,7 @@ public final class CraftServer implements Server {
         worlddata.checkName(name); // CraftBukkit - Migration did not rewrite the level.dat; This forces 1.8 to take the last loaded world as respawn (in this case the end)
         WorldServer internal = (WorldServer) new WorldServer(console, sdm, worlddata, dimension, console.methodProfiler, creator.environment(), generator).b();
 
-        if (!(worlds.containsKey(name.toLowerCase()))) {
+        if (!(worlds.containsKey(name.toLowerCase(java.util.Locale.ENGLISH)))) {
             return null;
         }
 
@@ -963,7 +963,7 @@ public final class CraftServer implements Server {
             }
         }
 
-        worlds.remove(world.getName().toLowerCase());
+        worlds.remove(world.getName().toLowerCase(java.util.Locale.ENGLISH));
         console.worlds.remove(console.worlds.indexOf(handle));
         return true;
     }
@@ -976,7 +976,7 @@ public final class CraftServer implements Server {
     public World getWorld(String name) {
         Validate.notNull(name, "Name cannot be null");
 
-        return worlds.get(name.toLowerCase());
+        return worlds.get(name.toLowerCase(java.util.Locale.ENGLISH));
     }
 
     @Override
@@ -995,7 +995,7 @@ public final class CraftServer implements Server {
             System.out.println("World " + world.getName() + " is a duplicate of another world and has been prevented from loading. Please delete the uid.dat file from " + world.getName() + "'s world directory if you want to be able to load the duplicate world.");
             return;
         }
-        worlds.put(world.getName().toLowerCase(), world);
+        worlds.put(world.getName().toLowerCase(java.util.Locale.ENGLISH), world);
     }
 
     @Override
diff --git a/src/main/java/org/bukkit/craftbukkit/attribute/CraftAttributeMap.java b/src/main/java/org/bukkit/craftbukkit/attribute/CraftAttributeMap.java
index 7c94acc5dd..e3adb5bda1 100644
--- a/src/main/java/org/bukkit/craftbukkit/attribute/CraftAttributeMap.java
+++ b/src/main/java/org/bukkit/craftbukkit/attribute/CraftAttributeMap.java
@@ -26,7 +26,7 @@ public class CraftAttributeMap implements Attributable {
         int first = bukkit.indexOf('_');
         int second = bukkit.indexOf('_', first + 1);
 
-        StringBuilder sb = new StringBuilder(bukkit.toLowerCase());
+        StringBuilder sb = new StringBuilder(bukkit.toLowerCase(java.util.Locale.ENGLISH));
 
         sb.setCharAt(first, '.');
         if (second != -1) {
diff --git a/src/main/java/org/bukkit/craftbukkit/block/CraftBlock.java b/src/main/java/org/bukkit/craftbukkit/block/CraftBlock.java
index 70099480cd..ed7e76ffa9 100644
--- a/src/main/java/org/bukkit/craftbukkit/block/CraftBlock.java
+++ b/src/main/java/org/bukkit/craftbukkit/block/CraftBlock.java
@@ -322,7 +322,7 @@ public class CraftBlock implements Block {
             return null;
         }
 
-        return Biome.valueOf(BiomeBase.REGISTRY_ID.b(base).a().toUpperCase());
+        return Biome.valueOf(BiomeBase.REGISTRY_ID.b(base).a().toUpperCase(java.util.Locale.ENGLISH));
     }
 
     public static BiomeBase biomeToBiomeBase(Biome bio) {
@@ -330,7 +330,7 @@ public class CraftBlock implements Block {
             return null;
         }
 
-        return BiomeBase.REGISTRY_ID.get(new MinecraftKey(bio.name().toLowerCase()));
+        return BiomeBase.REGISTRY_ID.get(new MinecraftKey(bio.name().toLowerCase(java.util.Locale.ENGLISH)));
     }
 
     public double getTemperature() {
diff --git a/src/main/java/org/bukkit/craftbukkit/metadata/PlayerMetadataStore.java b/src/main/java/org/bukkit/craftbukkit/metadata/PlayerMetadataStore.java
index d4d7f38b13..f4010b3a56 100644
--- a/src/main/java/org/bukkit/craftbukkit/metadata/PlayerMetadataStore.java
+++ b/src/main/java/org/bukkit/craftbukkit/metadata/PlayerMetadataStore.java
@@ -18,6 +18,6 @@ public class PlayerMetadataStore extends MetadataStoreBase<OfflinePlayer> implem
      */
     @Override
     protected String disambiguate(OfflinePlayer player, String metadataKey) {
-        return player.getName().toLowerCase() + ":" + metadataKey;
+        return player.getName().toLowerCase(java.util.Locale.ENGLISH) + ":" + metadataKey;
     }
 }
diff --git a/src/main/java/org/bukkit/craftbukkit/util/CraftChatMessage.java b/src/main/java/org/bukkit/craftbukkit/util/CraftChatMessage.java
index 38ef8216c4..560f95ccb6 100644
--- a/src/main/java/org/bukkit/craftbukkit/util/CraftChatMessage.java
+++ b/src/main/java/org/bukkit/craftbukkit/util/CraftChatMessage.java
@@ -57,7 +57,7 @@ public final class CraftChatMessage {
                 appendNewComponent(matcher.start(groupId));
                 switch (groupId) {
                 case 1:
-                    EnumChatFormat format = formatMap.get(match.toLowerCase().charAt(1));
+                    EnumChatFormat format = formatMap.get(match.toLowerCase(java.util.Locale.ENGLISH).charAt(1));
                     if (format == EnumChatFormat.RESET) {
                         modifier = new ChatModifier();
                     } else if (format.isFormat()) {
diff --git a/src/test/java/org/bukkit/SoundTest.java b/src/test/java/org/bukkit/SoundTest.java
index 2b00b4bf8b..8bb093daa9 100644
--- a/src/test/java/org/bukkit/SoundTest.java
+++ b/src/test/java/org/bukkit/SoundTest.java
@@ -21,7 +21,7 @@ public class SoundTest {
     @Test
     public void testReverse() {
         for (MinecraftKey effect : SoundEffect.a.keySet()) {
-            assertNotNull(effect + "", Sound.valueOf(effect.a().replace('.', '_').toUpperCase()));
+            assertNotNull(effect + "", Sound.valueOf(effect.a().replace('.', '_').toUpperCase(java.util.Locale.ENGLISH)));
         }
     }
 }