diff --git a/FortnoxAPILibrary/Entities/Invoice.cs b/FortnoxAPILibrary/Entities/Invoice.cs
index 6e6f323a..668c5673 100644
--- a/FortnoxAPILibrary/Entities/Invoice.cs
+++ b/FortnoxAPILibrary/Entities/Invoice.cs
@@ -48,6 +48,8 @@ public partial class Invoice
 
 		private string commentsField;
 
+        private string contractreferenceField;
+
 		private string contributionPercentField;
 
 		private string contributionValueField;
@@ -321,6 +323,16 @@ public string Comments
 			}
 		}
 
+        /// <remarks/>
+        public string ContractReference {
+            get {
+                return this.contractreferenceField;
+            }
+            set {
+                this.contractreferenceField = value;
+            }
+        }
+
 		/// <summary>This field is Read-Only in Fortnox</summary>
 		[ReadOnly(true)]
 		public string ContributionPercent
diff --git a/FortnoxAPILibrary/EntityConnector.cs b/FortnoxAPILibrary/EntityConnector.cs
index 11b4d6da..f2acfc9b 100644
--- a/FortnoxAPILibrary/EntityConnector.cs
+++ b/FortnoxAPILibrary/EntityConnector.cs
@@ -184,7 +184,8 @@ internal C BaseFind(Dictionary<string, string> parameters = null)
 
             if (this.LastModified != DateTime.MinValue)
             {
-                this.Parameters.Add("lastmodified", this.LastModified.ToString());
+                
+                this.Parameters.Add("lastmodified", this.LastModified.ToString("yyyy-MM-dd HH:mm:ss"));
             }
 
             if (this.SortByRealValue != null)