diff --git a/sql/api/src/main/scala/org/apache/spark/sql/types/DataType.scala b/sql/api/src/main/scala/org/apache/spark/sql/types/DataType.scala
index 23f058db022c8..96ba6612b35ea 100644
--- a/sql/api/src/main/scala/org/apache/spark/sql/types/DataType.scala
+++ b/sql/api/src/main/scala/org/apache/spark/sql/types/DataType.scala
@@ -460,7 +460,9 @@ object DataType {
       // String types with possibly different collations are compatible.
       case (CharType(l1), CharType(l2)) => l1 == l2
       case (VarcharType(l1), VarcharType(l2)) => l1 == l2
-      case (StringType, StringType) => true
+      case (CharType(_) | VarcharType(_), StringType) => false
+      case (StringType, CharType(_) | VarcharType(_)) => false
+      case (_: StringType, _: StringType) => true
 
       case (fromDataType, toDataType) => fromDataType == toDataType
     }