diff --git a/src/Nethermind/Nethermind.Serialization.Ssz.Test/MerkleTreeTests.cs b/src/Nethermind/Nethermind.Serialization.Ssz.Test/MerkleTreeTests.cs
index ae8125ce2d5..ce20f018783 100644
--- a/src/Nethermind/Nethermind.Serialization.Ssz.Test/MerkleTreeTests.cs
+++ b/src/Nethermind/Nethermind.Serialization.Ssz.Test/MerkleTreeTests.cs
@@ -34,7 +34,7 @@ public void Setup()
             }
         }
 
-        private MerkleTree BuildATree(IKeyValueStore<ulong, byte[]> keyValueStore = null)
+        private MerkleTree BuildATree(IKeyValueStore<ulong, byte[]>? keyValueStore = null)
         {
             return new ShaMerkleTree(keyValueStore ?? new MemMerkleTreeStore());
         }
@@ -222,7 +222,7 @@ public void On_adding_one_leaf_count_goes_up_to_1()
         [TestCase(123u)]
         public void Can_restore_count_from_the_database(uint leafCount)
         {
-            MemMerkleTreeStore memDb = new MemMerkleTreeStore();
+            MemMerkleTreeStore? memDb = new MemMerkleTreeStore();
             MerkleTree baselineTree = BuildATree(memDb);
 
             for (int i = 0; i < leafCount; i++)
diff --git a/src/Nethermind/Nethermind.Serialization.Ssz.Test/Nethermind.Serialization.Ssz.Test.csproj b/src/Nethermind/Nethermind.Serialization.Ssz.Test/Nethermind.Serialization.Ssz.Test.csproj
index 0f798395f5b..4e18af30341 100644
--- a/src/Nethermind/Nethermind.Serialization.Ssz.Test/Nethermind.Serialization.Ssz.Test.csproj
+++ b/src/Nethermind/Nethermind.Serialization.Ssz.Test/Nethermind.Serialization.Ssz.Test.csproj
@@ -5,6 +5,7 @@
     <LangVersion>latest</LangVersion>
     <IsPackable>false</IsPackable>
     <Nullable>enable</Nullable>
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
   </PropertyGroup>
 
   <ItemGroup>