diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/CheckAnalysis.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/CheckAnalysis.scala
index f104e742c90f..b51880dceaf5 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/CheckAnalysis.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/CheckAnalysis.scala
@@ -105,6 +105,12 @@ trait CheckAnalysis {
 
             cleaned.foreach(checkValidAggregateExpression)
 
+          case u @ Union(left, right) if left.output.size != right.output.size =>
+            failAnalysis(
+              s"union's left child and right child have different output size. " +
+                s"union node: $u left output size: ${left.output.size}, " +
+                  s"right output size: ${right.output.size}")
+
           case _ => // Fallbacks to the following checks
         }