diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/arithmetic.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/arithmetic.scala
index 116227224fdd1..8fb597155fcb1 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/arithmetic.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/arithmetic.scala
@@ -481,12 +481,12 @@ case class Add(
     // TODO: do not reorder consecutive `Add`s with different `evalMode`
     val reorderResult =
       orderCommutative({ case Add(l, r, _) => Seq(l, r) }).reduce(Add(_, _, evalMode))
-    if (resolved && reorderResult.resolved && reorderResult.dataType == dataType) {
-      reorderResult
+    if (resolved && reorderResult.resolved && reorderResult.dataType != dataType) {
+      // SPARK-40903: Append cast for the canonicalization of decimal Add if the result data type is
+      // changed. Otherwise, it may cause data checking error within ComplexTypeMergingExpression.
+      Cast(reorderResult, dataType)
     } else {
-      // SPARK-40903: Avoid reordering decimal Add for canonicalization if the result data type is
-      // changed, which may cause data checking error within ComplexTypeMergingExpression.
-      withCanonicalizedChildren
+      reorderResult
     }
   }
 }
diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/CanonicalizeSuite.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/CanonicalizeSuite.scala
index 057fb98c23985..35ed48855080a 100644
--- a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/CanonicalizeSuite.scala
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/CanonicalizeSuite.scala
@@ -206,4 +206,16 @@ class CanonicalizeSuite extends SparkFunSuite {
     assert(!Add(Add(literal4, literal5), literal1).semanticEquals(
       Add(Add(literal1, literal5), literal4)))
   }
+
+  test("SPARK-40903: Append Casting if the canonicalization result type is changed") {
+    val d = Decimal(1.2)
+    val literal1 = Literal.create(d, DecimalType(2, 1))
+    val literal2 = Literal.create(d, DecimalType(12, 5))
+    val literal3 = Literal.create(d, DecimalType(12, 6))
+    val add1 = Add(literal1, Add(literal2, literal3)).canonicalized
+    val add2 = Add(Add(literal3, literal2), literal1).canonicalized
+    assert(add1.isInstanceOf[Cast] && add1.dataType == DecimalType(15, 6))
+    assert(add2.isInstanceOf[Cast] && add2.dataType == DecimalType(15, 6))
+    assert(add1 == add2)
+  }
 }