diff --git a/QueryBuilder/Base.Where.cs b/QueryBuilder/Base.Where.cs
index 62eb5145..02f8f498 100644
--- a/QueryBuilder/Base.Where.cs
+++ b/QueryBuilder/Base.Where.cs
@@ -581,7 +581,7 @@ public Q WhereDatePart(string part, string column, string op, object value)
                 Operator = op,
                 Column = column,
                 Value = value,
-                Part = part,
+                Part = part?.ToLowerInvariant(),
                 IsOr = GetOr(),
                 IsNot = GetNot(),
             });