diff --git a/go/vt/schemadiff/diff_test.go b/go/vt/schemadiff/diff_test.go
index aa323cec792..6f189d85c71 100644
--- a/go/vt/schemadiff/diff_test.go
+++ b/go/vt/schemadiff/diff_test.go
@@ -296,6 +296,17 @@ func TestDiffSchemas(t *testing.T) {
 			from: "create table t(id int primary key)",
 			to:   "create table t(id int primary key)",
 		},
+		{
+			name: "change of table column",
+			from: "create table t(id int primary key, v varchar(10))",
+			to:   "create table t(id int primary key, v varchar(20))",
+			diffs: []string{
+				"alter table t modify column v varchar(20)",
+			},
+			cdiffs: []string{
+				"ALTER TABLE `t` MODIFY COLUMN `v` varchar(20)",
+			},
+		},
 		{
 			name: "change of table columns, added",
 			from: "create table t(id int primary key)",
@@ -329,7 +340,7 @@ func TestDiffSchemas(t *testing.T) {
 			},
 		},
 		{
-			name: "create table (2)",
+			name: "create table 2",
 			from: ";;; ; ;    ;;;",
 			to:   "create table t(id int primary key)",
 			diffs: []string{
@@ -501,11 +512,16 @@ func TestDiffSchemas(t *testing.T) {
 					// Validate "apply()" on "from" converges with "to"
 					schema1, err := NewSchemaFromSQL(ts.from)
 					assert.NoError(t, err)
+					schema1SQL := schema1.ToSQL()
+
 					schema2, err := NewSchemaFromSQL(ts.to)
 					assert.NoError(t, err)
 					applied, err := schema1.Apply(diffs)
 					require.NoError(t, err)
 
+					// validate schema1 unaffected by Apply
+					assert.Equal(t, schema1SQL, schema1.ToSQL())
+
 					appliedDiff, err := schema2.Diff(applied, hints)
 					require.NoError(t, err)
 					assert.Empty(t, appliedDiff)
diff --git a/go/vt/schemadiff/schema.go b/go/vt/schemadiff/schema.go
index 916a1d37fcc..940ecd1571c 100644
--- a/go/vt/schemadiff/schema.go
+++ b/go/vt/schemadiff/schema.go
@@ -426,7 +426,11 @@ func (s *Schema) apply(diffs []EntityDiff) error {
 // These diffs are CREATE/DROP/ALTER TABLE/VIEW.
 // The operation does not modify this object. Instead, if successful, a new (modified) Schema is returned.
 func (s *Schema) Apply(diffs []EntityDiff) (*Schema, error) {
-	dup, err := NewSchemaFromStatements(s.ToStatements())
+	// we export to queries, then import back.
+	// The reason we don't just clone this object's fields, or even export/import to Statements,
+	// is that we want this schema to be immutable an unaffected by the apply() on the duplicate.
+	// statements/slices/maps will have shared pointers and changes will propagate back to this schema.
+	dup, err := NewSchemaFromQueries(s.ToQueries())
 	if err != nil {
 		return nil, err
 	}