diff --git a/FastCache/FastCache.cs b/FastCache/FastCache.cs
index bfd1b09..88e7c64 100644
--- a/FastCache/FastCache.cs
+++ b/FastCache/FastCache.cs
@@ -184,7 +184,30 @@ public TValue GetOrAdd(TKey key, Func<TKey, TValue> valueFactory, TimeSpan ttl)
 			if (TryGet(key, out var value))
 				return value;
 
-			return _dict.GetOrAdd(key, (k, v) => new TtlValue(v.valueFactory(k), v.ttl), (ttl, valueFactory)).Value;
+			return _dict.GetOrAdd(
+				key,
+				(k, arg) => new TtlValue(arg.valueFactory(k), arg.ttl),
+				(ttl, valueFactory)
+			).Value;
+		}
+
+		/// <summary>
+		/// Adds a key/value pair by using the specified function if the key does not already exist, or returns the existing value if the key exists.
+		/// </summary>
+		/// <param name="key">The key to add</param>
+		/// <param name="valueFactory">The factory function used to generate the item for the key</param>
+		/// <param name="ttl">TTL of the item</param>
+		/// <param name="factoryArgument">Argument value to pass into valueFactory</param>
+		public TValue GetOrAdd<TArg>(TKey key, Func<TKey, TArg, TValue> valueFactory, TimeSpan ttl, TArg factoryArgument)
+		{
+			if (TryGet(key, out var value))
+				return value;
+
+			return _dict.GetOrAdd(
+				key,
+				(k, arg) => new TtlValue(arg.valueFactory(k, arg.factoryArgument), arg.ttl),
+				(ttl, valueFactory, factoryArgument)
+			).Value;
 		}
 
 		/// <summary>
diff --git a/UnitTests/UnitTests.cs b/UnitTests/UnitTests.cs
index 8a9accf..91be0b9 100644
--- a/UnitTests/UnitTests.cs
+++ b/UnitTests/UnitTests.cs
@@ -123,6 +123,18 @@ public async Task TestGetOrAdd()
 			Assert.IsFalse(cache.TryGet("key", out _));
 		}
 
+		[TestMethod]
+		public async Task TestGetOrAddWithArg()
+		{
+			var cache = new FastCache<string, int>();
+			cache.GetOrAdd("key", (k, arg) => 1024 + arg.Length, TimeSpan.FromMilliseconds(100), "test123");
+			Assert.IsTrue(cache.TryGet("key", out int res) && res == 1031);
+
+			//eviction
+			await Task.Delay(110);
+			Assert.IsFalse(cache.TryGet("key", out _));
+		}
+
 		[TestMethod]
 		public void TestClear()
 		{