diff --git a/src/main/java/codechicken/lib/render/pipeline/IVertexOperation.java b/src/main/java/codechicken/lib/render/pipeline/IVertexOperation.java
index a8a4c247..00b74a87 100644
--- a/src/main/java/codechicken/lib/render/pipeline/IVertexOperation.java
+++ b/src/main/java/codechicken/lib/render/pipeline/IVertexOperation.java
@@ -8,7 +8,7 @@
 public interface IVertexOperation {
 
     static int registerOperation() {
-        return VertexOperationRegistry.nextOperationIndex++;
+        return VertexOperationRegistry.nextOperationIndex();
     }
 
     static int operationCount() {
@@ -35,5 +35,9 @@ static int operationCount() {
     class VertexOperationRegistry {
 
         static int nextOperationIndex;
+
+        private static synchronized int nextOperationIndex() {
+            return VertexOperationRegistry.nextOperationIndex++;
+        }
     }
 }
diff --git a/src/main/java/codechicken/lib/render/pipeline/attribute/AttributeKey.java b/src/main/java/codechicken/lib/render/pipeline/attribute/AttributeKey.java
index 6c35d681..2cc2a4a3 100644
--- a/src/main/java/codechicken/lib/render/pipeline/attribute/AttributeKey.java
+++ b/src/main/java/codechicken/lib/render/pipeline/attribute/AttributeKey.java
@@ -93,7 +93,7 @@ public static class AttributeKeyRegistry {
         private static final Map<String, AttributeKey<?>> nameMap = new HashMap<>();
         private static final List<AttributeKey<?>> attributeKeys = new ArrayList<>();
 
-        private static int registerAttributeKey(AttributeKey<?> attr) {
+        private static synchronized int registerAttributeKey(AttributeKey<?> attr) {
             if (nameMap.containsKey(attr.name)) {
                 throw new IllegalArgumentException("Duplicate registration of attribute with name: " + attr.name);
             }