diff --git a/TODO b/TODO
index 7324834..4429109 100644
--- a/TODO
+++ b/TODO
@@ -1,4 +1,4 @@
 - look at test coverage
 - docs
 
-- WritesPending and writes redundant?
\ No newline at end of file
+- make sure two different engines that Write the same component cannot have same priority
\ No newline at end of file
diff --git a/encompass-cs/WorldBuilder.cs b/encompass-cs/WorldBuilder.cs
index 1e8de7e..74bb81d 100644
--- a/encompass-cs/WorldBuilder.cs
+++ b/encompass-cs/WorldBuilder.cs
@@ -186,6 +186,8 @@ namespace Encompass
             var writtenComponentTypesWithoutPriority = new HashSet<Type>();
             var writtenComponentTypesWithPriority = new HashSet<Type>();
             var duplicateWritesWithoutPriority = new List<Type>();
+            var duplicateWritesWithSamePriority = new List<Type>();
+            var writePriorities = new Dictionary<Type, HashSet<int>>();
             var writeMessageToEngines = new Dictionary<Type, List<Engine>>();
 
             foreach (var engine in engines)
@@ -196,7 +198,31 @@ namespace Encompass
                 {
                     var componentType = writeType.GetGenericArguments()[0];
 
-                    if (!engine.writePriorities.ContainsKey(componentType))
+                    if (engine.writePriorities.ContainsKey(componentType))
+                    {
+                        var priority = engine.writePriorities[componentType];
+
+                        writtenComponentTypesWithPriority.Add(componentType);
+
+                        if (!writePriorities.ContainsKey(componentType))
+                        {
+                            writePriorities[componentType] = new HashSet<int>();
+                        }
+
+                        if (writePriorities[componentType].Contains(priority))
+                        {
+                            duplicateWritesWithSamePriority.Add(componentType);
+                        }
+                        else if (writtenComponentTypesWithoutPriority.Contains(componentType))
+                        {
+                            duplicateWritesWithoutPriority.Add(componentType);
+                        }
+                        else
+                        {
+                            writePriorities[componentType].Add(priority);
+                        }
+                    }
+                    else
                     {
                         if (writtenComponentTypesWithoutPriority.Contains(componentType) || writtenComponentTypesWithPriority.Contains(componentType))
                         {
@@ -207,10 +233,6 @@ namespace Encompass
                             writtenComponentTypesWithoutPriority.Add(componentType);
                         }
                     }
-                    else
-                    {
-                        writtenComponentTypesWithPriority.Add(componentType);
-                    }
 
                     if (!writeMessageToEngines.ContainsKey(componentType))
                     {
@@ -235,6 +257,20 @@ namespace Encompass
                 throw new EngineWriteConflictException(errorString);
             }
 
+            if (duplicateWritesWithSamePriority.Count > 0)
+            {
+                var errorString = "Multiple Engines write the same Component with the same priority: ";
+                foreach (var componentType in duplicateWritesWithSamePriority)
+                {
+                    errorString += "\n" +
+                    componentType.Name + " written by: " +
+                    string.Join(", ", writeMessageToEngines[componentType].Select(engine => engine.GetType().Name));
+                }
+                errorString += "\nTo resolve the conflict, add priority arguments to the Writes declarations.";
+
+                throw new EngineWriteConflictException(errorString);
+            }
+
             var engineOrder = new List<Engine>();
             foreach (var engine in engineGraph.TopologicalSort())
             {
diff --git a/test/WorldBuilderTest.cs b/test/WorldBuilderTest.cs
index a93b1b5..32d1207 100644
--- a/test/WorldBuilderTest.cs
+++ b/test/WorldBuilderTest.cs
@@ -275,6 +275,68 @@ namespace Tests
             }
         }
 
+        public class PriorityConflict
+        {
+            [Writes(typeof(MockComponent), 2)]
+            class AEngine : Engine
+            {
+                public override void Update(double dt)
+                {
+
+                }
+            }
+
+            [Writes(typeof(MockComponent), 2)]
+            class BEngine : Engine
+            {
+                public override void Update(double dt)
+                {
+
+                }
+            }
+
+            [Test]
+            public void PriorityConflictTest()
+            {
+                var worldBuilder = new WorldBuilder();
+                worldBuilder.AddEngine(new AEngine());
+                worldBuilder.AddEngine(new BEngine());
+
+                Assert.Throws<EngineWriteConflictException>(() => worldBuilder.Build());
+            }
+        }
+
+        public class EngineWriteConflict
+        {
+            [Writes(typeof(MockComponent))]
+            class AEngine : Engine
+            {
+                public override void Update(double dt)
+                {
+
+                }
+            }
+
+            [Writes(typeof(MockComponent), 2)]
+            class BEngine : Engine
+            {
+                public override void Update(double dt)
+                {
+
+                }
+            }
+
+            [Test]
+            public void EngineWriteConflictPriorityAndNoPriorityTest()
+            {
+                var worldBuilder = new WorldBuilder();
+                worldBuilder.AddEngine(new AEngine());
+                worldBuilder.AddEngine(new BEngine());
+
+                Assert.Throws<EngineWriteConflictException>(() => worldBuilder.Build());
+            }
+        }
+
         public class LegalEngines
         {
             static List<Engine> order = new List<Engine>();