diff --git a/core/src/main/java/org/apache/iceberg/schema/UnionByNameVisitor.java b/core/src/main/java/org/apache/iceberg/schema/UnionByNameVisitor.java
index fa2efac0ee54..f3780d17bd69 100644
--- a/core/src/main/java/org/apache/iceberg/schema/UnionByNameVisitor.java
+++ b/core/src/main/java/org/apache/iceberg/schema/UnionByNameVisitor.java
@@ -20,7 +20,6 @@
 
 import java.util.List;
 import java.util.stream.Collectors;
-import java.util.stream.Stream;
 import org.apache.iceberg.Schema;
 import org.apache.iceberg.UpdateSchema;
 import org.apache.iceberg.relocated.com.google.common.base.Preconditions;
@@ -29,9 +28,9 @@
 
 /**
  * Visitor class that accumulates the set of changes needed to evolve an existing schema into the
- * union of the existing and a new schema. If all old elements of the schema are present in the
- * new schema in the same order as the existing schema, places new elements in the same places as
- * they exist in the new schema. Changes are added to an {@link UpdateSchema} operation.
+ * union of the existing and a new schema. If all old elements of the schema are present in the new
+ * schema in the same order as the existing schema, places new elements in the same places as they
+ * exist in the new schema. Changes are added to an {@link UpdateSchema} operation.
  */
 public class UnionByNameVisitor extends SchemaWithPartnerVisitor<Integer, Boolean> {
 
@@ -102,9 +101,9 @@ public Boolean struct(
       } else {
         lastPartnerField += 1;
         Types.NestedField nestedField =
-                caseSensitive
-                        ? partnerStruct.field(field.name())
-                        : partnerStruct.caseInsensitiveField(field.name());
+            caseSensitive
+                ? partnerStruct.field(field.name())
+                : partnerStruct.caseInsensitiveField(field.name());
         updateColumn(field, nestedField);
       }
     }
@@ -164,10 +163,12 @@ private Type findFieldType(int fieldId) {
     }
   }
 
-  private boolean nonMissingElementsInOrder(Types.StructType oldStruct, Types.StructType newStruct) {
+  private boolean nonMissingElementsInOrder(
+      Types.StructType oldStruct, Types.StructType newStruct) {
     List<String> oldFields =
         oldStruct.fields().stream().map(Types.NestedField::name).collect(Collectors.toList());
-    List<String> newFields = newStruct.fields().stream().map(Types.NestedField::name).collect(Collectors.toList());
+    List<String> newFields =
+        newStruct.fields().stream().map(Types.NestedField::name).collect(Collectors.toList());
 
     newFields.retainAll(oldFields);
 
@@ -182,7 +183,11 @@ private void addColumnBefore(int parentId, Types.NestedField field, Types.Nested
     String parentName = partnerSchema.findColumnName(parentId);
     api.addColumn(parentName, field.name(), field.type(), field.doc());
     if (nextField != null) {
-      api.moveBefore(parentName + "." + field.name(), parentName + "." + nextField.name());
+      if (parentName != null) {
+        api.moveBefore(parentName + "." + field.name(), parentName + "." + nextField.name());
+      } else {
+        api.moveBefore(field.name(), nextField.name());
+      }
     }
   }
 
diff --git a/core/src/test/java/org/apache/iceberg/TestSchemaUnionByFieldName.java b/core/src/test/java/org/apache/iceberg/TestSchemaUnionByFieldName.java
index 214f49952278..19528610cc88 100644
--- a/core/src/test/java/org/apache/iceberg/TestSchemaUnionByFieldName.java
+++ b/core/src/test/java/org/apache/iceberg/TestSchemaUnionByFieldName.java
@@ -581,22 +581,38 @@ public void testAppendNestedLists() {
 
   @Test
   public void testInsertNestedPrimitiveIntoMiddleOfStruct() {
-    Schema currentSchema = new Schema(optional(1, "aStruct", Types.StructType.of(
-            optional(2, "string", Types.StringType.get()),
-            optional(3, "long", Types.StringType.get()),
-            optional( 4, "substruct", Types.StructType.of(
-                    optional(5, "deepint", Types.IntegerType.get()))))));
-
-    Schema newSchema = new Schema(optional(1, "aStruct", Types.StructType.of(
-            optional(2, "string", Types.StringType.get()),
-            optional(8, "string2", Types.StringType.get()),
-            optional(9, "string3", Types.StringType.get()),
-            optional(3, "long", Types.StringType.get()),
-            optional( 4, "substruct", Types.StructType.of(
-                    optional( 6, "firstnewdeepInt", Types.IntegerType.get()),
-                    optional( 7, "newdeepInt", Types.IntegerType.get()),
-                    optional(5, "deepint", Types.IntegerType.get()))),
-            optional(10, "lastint", Types.IntegerType.get()))));
+    Schema currentSchema =
+        new Schema(
+            optional(
+                1,
+                "aStruct",
+                Types.StructType.of(
+                    optional(2, "string", Types.StringType.get()),
+                    optional(3, "long", Types.StringType.get()),
+                    optional(
+                        4,
+                        "substruct",
+                        Types.StructType.of(optional(5, "deepint", Types.IntegerType.get()))))));
+
+    Schema newSchema =
+        new Schema(
+            optional(11, "newfirstColumn", Types.IntegerType.get()),
+            optional(
+                1,
+                "aStruct",
+                Types.StructType.of(
+                    optional(2, "string", Types.StringType.get()),
+                    optional(8, "string2", Types.StringType.get()),
+                    optional(9, "string3", Types.StringType.get()),
+                    optional(3, "long", Types.StringType.get()),
+                    optional(
+                        4,
+                        "substruct",
+                        Types.StructType.of(
+                            optional(6, "firstnewdeepInt", Types.IntegerType.get()),
+                            optional(7, "newdeepInt", Types.IntegerType.get()),
+                            optional(5, "deepint", Types.IntegerType.get()))),
+                    optional(10, "lastint", Types.IntegerType.get()))));
 
     Schema applied = new SchemaUpdate(currentSchema, 5).unionByNameWith(newSchema).apply();
     Assert.assertEquals(newSchema.asStruct(), applied.asStruct());
@@ -604,26 +620,39 @@ public void testInsertNestedPrimitiveIntoMiddleOfStruct() {
 
   @Test
   public void testInsertNestedPrimitiveOriginalFieldsOOOrder() {
-    Schema currentSchema = new Schema(optional(1, "aStruct", Types.StructType.of(
-            optional(2, "field1", Types.StringType.get()),
-            optional(3, "field2", Types.StringType.get()),
-            optional( 4, "field3", Types.StringType.get()))));
-
-    Schema newSchema = new Schema(optional(1, "aStruct", Types.StructType.of(
-            optional(5, "field4", Types.StringType.get()),
-            optional(3, "field2", Types.StringType.get()),
-            optional(4, "field3", Types.StringType.get()),
-            optional(2, "field1", Types.StringType.get()))));
+    Schema currentSchema =
+        new Schema(
+            optional(
+                1,
+                "aStruct",
+                Types.StructType.of(
+                    optional(2, "field1", Types.StringType.get()),
+                    optional(3, "field2", Types.StringType.get()),
+                    optional(4, "field3", Types.StringType.get()))));
 
-    Schema expectedSchema = new Schema(optional(1, "aStruct", Types.StructType.of(
-            optional(2, "field1", Types.StringType.get()),
-            optional(3, "field2", Types.StringType.get()),
-            optional(4, "field3", Types.StringType.get()),
-            optional(5, "field4", Types.StringType.get()))));
+    Schema newSchema =
+        new Schema(
+            optional(
+                1,
+                "aStruct",
+                Types.StructType.of(
+                    optional(5, "field4", Types.StringType.get()),
+                    optional(3, "field2", Types.StringType.get()),
+                    optional(4, "field3", Types.StringType.get()),
+                    optional(2, "field1", Types.StringType.get()))));
 
+    Schema expectedSchema =
+        new Schema(
+            optional(
+                1,
+                "aStruct",
+                Types.StructType.of(
+                    optional(2, "field1", Types.StringType.get()),
+                    optional(3, "field2", Types.StringType.get()),
+                    optional(4, "field3", Types.StringType.get()),
+                    optional(5, "field4", Types.StringType.get()))));
 
     Schema applied = new SchemaUpdate(currentSchema, 4).unionByNameWith(newSchema).apply();
     Assert.assertEquals(expectedSchema.asStruct(), applied.asStruct());
   }
-
 }