diff --git a/src/NexusMods.MnemonicDB.Abstractions/Attribute.cs b/src/NexusMods.MnemonicDB.Abstractions/Attribute.cs
index b04d1046..e5174599 100644
--- a/src/NexusMods.MnemonicDB.Abstractions/Attribute.cs
+++ b/src/NexusMods.MnemonicDB.Abstractions/Attribute.cs
@@ -66,6 +66,14 @@ protected virtual TValueType FromLowLevel(ushort value, ValueTags tags)
         throw new NotSupportedException("Unsupported low-level type " + value + " on attribute " + Id);
     }
 
+    /// <summary>
+    /// Converts a low-level value to a high-level value
+    /// </summary>
+    protected virtual TValueType FromLowLevel(uint value, ValueTags tags)
+    {
+        throw new NotSupportedException("Unsupported low-level type " + value + " on attribute " + Id);
+    }
+
 
     /// <summary>
     /// Converts a low-level value to a high-level value
@@ -331,6 +339,7 @@ public TValueType ReadValue(ReadOnlySpan<byte> span)
             ValueTags.Null => NullFromLowLevel(),
             ValueTags.UInt8 => FromLowLevel(ReadUnmanaged<byte>(rest), tag),
             ValueTags.UInt16 => FromLowLevel(ReadUnmanaged<ushort>(rest), tag),
+            ValueTags.UInt32 => FromLowLevel(ReadUnmanaged<uint>(rest), tag),
             ValueTags.UInt64 => FromLowLevel(ReadUnmanaged<ulong>(rest), tag),
             ValueTags.UInt128 => FromLowLevel(ReadUnmanaged<UInt128>(rest), tag),
             ValueTags.Int16 => FromLowLevel(ReadUnmanaged<short>(rest), tag),
diff --git a/src/NexusMods.MnemonicDB.Abstractions/Attributes/UnknownAttribute.cs b/src/NexusMods.MnemonicDB.Abstractions/Attributes/UnknownAttribute.cs
new file mode 100644
index 00000000..3148d2fa
--- /dev/null
+++ b/src/NexusMods.MnemonicDB.Abstractions/Attributes/UnknownAttribute.cs
@@ -0,0 +1,166 @@
+using System;
+using NexusMods.MnemonicDB.Abstractions.ElementComparers;
+
+namespace NexusMods.MnemonicDB.Abstractions.Attributes;
+
+/// <summary>
+/// An unknown attribute is an attribute that exists in the database but is not known to the application. This is
+/// either because the attribute was removed, or didn't show up in the DI system.
+/// </summary>
+/// <param name="dbAttribute"></param>
+/// <typeparam name="TLowLevel"></typeparam>
+public class UnknownAttribute<TLowLevel>(DbAttribute dbAttribute) :
+    Attribute<TLowLevel, TLowLevel>(dbAttribute.LowLevelType, dbAttribute.UniqueId.Namespace, dbAttribute.UniqueId.Name)
+{
+    /// <inheritdoc />
+    protected override TLowLevel ToLowLevel(TLowLevel value)
+    {
+        return value;
+    }
+
+    /// <inheritdoc />
+    protected override TLowLevel FromLowLevel(byte value, ValueTags tags)
+    {
+        if (tags != LowLevelType)
+        {
+            throw new ArgumentException($"Cannot convert {tags} to {LowLevelType}");
+        }
+
+        return (TLowLevel)(object)value;
+    }
+
+    /// <inheritdoc />
+    protected override TLowLevel FromLowLevel(ushort value, ValueTags tags)
+    {
+        if (tags != LowLevelType)
+        {
+            throw new ArgumentException($"Cannot convert {tags} to {LowLevelType}");
+        }
+
+        return (TLowLevel)(object)value;
+    }
+
+    /// <inheritdoc />
+    protected override TLowLevel FromLowLevel(uint value, ValueTags tags)
+    {
+        if (tags != LowLevelType)
+        {
+            throw new ArgumentException($"Cannot convert {tags} to {LowLevelType}");
+        }
+
+        return (TLowLevel)(object)value;
+    }
+
+
+    /// <inheritdoc />
+    protected override TLowLevel FromLowLevel(ulong value, ValueTags tags)
+    {
+        if (tags != LowLevelType)
+        {
+            throw new ArgumentException($"Cannot convert {tags} to {LowLevelType}");
+        }
+
+        return (TLowLevel)(object)value;
+    }
+
+    /// <inheritdoc />
+    protected override TLowLevel FromLowLevel(short value, ValueTags tags)
+    {
+        if (tags != LowLevelType)
+        {
+            throw new ArgumentException($"Cannot convert {tags} to {LowLevelType}");
+        }
+
+        return (TLowLevel)(object)value;
+    }
+
+    /// <inheritdoc />
+    protected override TLowLevel FromLowLevel(int value, ValueTags tags)
+    {
+        if (tags != LowLevelType)
+        {
+            throw new ArgumentException($"Cannot convert {tags} to {LowLevelType}");
+        }
+
+        return (TLowLevel)(object)value;
+    }
+
+    /// <inheritdoc />
+    protected override TLowLevel FromLowLevel(long value, ValueTags tags)
+    {
+        if (tags != LowLevelType)
+        {
+            throw new ArgumentException($"Cannot convert {tags} to {LowLevelType}");
+        }
+
+        return (TLowLevel)(object)value;
+    }
+
+    /// <inheritdoc />
+    protected override TLowLevel FromLowLevel(float value, ValueTags tags)
+    {
+        if (tags != LowLevelType)
+        {
+            throw new ArgumentException($"Cannot convert {tags} to {LowLevelType}");
+        }
+
+        return (TLowLevel)(object)value;
+    }
+
+    /// <inheritdoc />
+    protected override TLowLevel FromLowLevel(double value, ValueTags tags)
+    {
+        if (tags != LowLevelType)
+        {
+            throw new ArgumentException($"Cannot convert {tags} to {LowLevelType}");
+        }
+
+        return (TLowLevel)(object)value;
+    }
+
+    /// <inheritdoc />
+    protected override TLowLevel FromLowLevel(string value, ValueTags tags)
+    {
+        if (tags != LowLevelType)
+        {
+            throw new ArgumentException($"Cannot convert {tags} to {LowLevelType}");
+        }
+
+        return (TLowLevel)(object)value;
+    }
+}
+
+/// <summary>
+/// Helper class to create unknown attributes
+/// </summary>
+public static class UnknownAttribute
+{
+    /// <summary>
+    /// Creates an unknown attribute from a database attribute
+    /// </summary>
+    public static IAttribute Create(DbAttribute dbAttribute)
+    {
+        return dbAttribute.LowLevelType switch
+        {
+            ValueTags.Null => new UnknownAttribute<Null>(dbAttribute),
+            ValueTags.UInt8 => new UnknownAttribute<byte>(dbAttribute),
+            ValueTags.UInt16 => new UnknownAttribute<ushort>(dbAttribute),
+            ValueTags.UInt32 => new UnknownAttribute<uint>(dbAttribute),
+            ValueTags.UInt64 => new UnknownAttribute<ulong>(dbAttribute),
+            ValueTags.UInt128 => new UnknownAttribute<ulong>(dbAttribute),
+            ValueTags.Int16 => new UnknownAttribute<short>(dbAttribute),
+            ValueTags.Int32 => new UnknownAttribute<int>(dbAttribute),
+            ValueTags.Int64 => new UnknownAttribute<long>(dbAttribute),
+            ValueTags.Int128 => new UnknownAttribute<long>(dbAttribute),
+            ValueTags.Float32 => new UnknownAttribute<float>(dbAttribute),
+            ValueTags.Float64 => new UnknownAttribute<double>(dbAttribute),
+            ValueTags.Ascii => new UnknownAttribute<string>(dbAttribute),
+            ValueTags.Utf8 => new UnknownAttribute<string>(dbAttribute),
+            ValueTags.Utf8Insensitive => new UnknownAttribute<string>(dbAttribute),
+            ValueTags.Blob => new UnknownAttribute<byte[]>(dbAttribute),
+            ValueTags.HashedBlob => new UnknownAttribute<byte[]>(dbAttribute),
+            ValueTags.Reference => new UnknownAttribute<EntityId>(dbAttribute),
+            _ => throw new ArgumentOutOfRangeException(nameof(dbAttribute.LowLevelType), dbAttribute.LowLevelType, null)
+        };
+    }
+}
diff --git a/src/NexusMods.MnemonicDB.Storage/AttributeRegistry.cs b/src/NexusMods.MnemonicDB.Storage/AttributeRegistry.cs
index 8fde023f..265a081a 100644
--- a/src/NexusMods.MnemonicDB.Storage/AttributeRegistry.cs
+++ b/src/NexusMods.MnemonicDB.Storage/AttributeRegistry.cs
@@ -5,6 +5,7 @@
 using System.Runtime.InteropServices;
 using System.Threading;
 using NexusMods.MnemonicDB.Abstractions;
+using NexusMods.MnemonicDB.Abstractions.Attributes;
 using NexusMods.MnemonicDB.Abstractions.Internals;
 using Reloaded.Memory.Extensions;
 
@@ -69,6 +70,7 @@ public AttributeRegistry(IEnumerable<IAttribute> attributes)
     /// <inheritdoc />
     public RegistryId Id { get; }
 
+    /// <inheritdoc />
     public IReadDatom Resolve(ReadOnlySpan<byte> datom)
     {
         var c = MemoryMarshal.Read<KeyPrefix>(datom);
@@ -77,11 +79,18 @@ public IReadDatom Resolve(ReadOnlySpan<byte> datom)
         return attr.Resolve(c.E, c.A, datom.SliceFast(KeyPrefix.Size), c.T, c.IsRetract);
     }
 
+    /// <inheritdoc />
     public void Populate(DbAttribute[] attributes)
     {
         foreach (var dbAttribute in attributes)
         {
-            var instance = _attributesBySymbol[dbAttribute.UniqueId];
+            // Do a try/get here because an attribute may not exist in code that exists in the database
+            if (!_attributesBySymbol.TryGetValue(dbAttribute.UniqueId, out var instance))
+            {
+                instance = UnknownAttribute.Create(dbAttribute);
+                _attributesBySymbol[dbAttribute.UniqueId] = instance;
+            }
+
             instance.SetDbId(Id, dbAttribute.AttrEntityId);
             _attributes[dbAttribute.AttrEntityId.Value] = instance;
         }