diff --git a/deserialize/deserialize.go b/deserialize/deserialize.go
index b2dc0f3..3004e5e 100644
--- a/deserialize/deserialize.go
+++ b/deserialize/deserialize.go
@@ -743,7 +743,9 @@ func makeStructDeserializerFromReflect(path string, typ reflect.Type, options in
 			mightValidate := resultPtr.Interface()
 			if validator, ok := mightValidate.(validation.Validator); ok {
 				err = validator.Validate()
-				if err != nil {
+				if err == nil {
+					outPtr.Set(result) // Note: Wait, are we copying everything here?
+				} else {
 					// Validation error, abort struct construction, wrap the error so that we can catch it.
 					err = validation.WrapError(path, err)
 					result = reflect.Zero(typ)
diff --git a/deserialize/deserialize_test.go b/deserialize/deserialize_test.go
index cd709fe..55eb3cf 100644
--- a/deserialize/deserialize_test.go
+++ b/deserialize/deserialize_test.go
@@ -1580,3 +1580,26 @@ func TestKVDeserializeUnderlyingPrimitiveSlices(t *testing.T) {
 	assert.NilError(t, err)
 	assert.DeepEqual(t, *deserialized, sample)
 }
+
+// --- Testing side-effects during validation.
+
+type TestValidateModifyStruct struct {
+	A string
+}
+
+func (t *TestValidateModifyStruct) Validate() error {
+	t.A = strings.ToLower(t.A)
+	return nil
+}
+
+func TestValidateModify(t *testing.T) {
+	kvlist := make(map[string][]string)
+	kvlist["A"] = []string{"ABC"}
+
+	deserializer, err := deserialize.MakeKVListDeserializer[TestValidateModifyStruct](deserialize.JSONOptions(""))
+	assert.NilError(t, err)
+	deserialized, err := deserializer.DeserializeKVList(kvlist)
+	assert.NilError(t, err)
+	fmt.Println(*deserialized)
+	assert.Equal(t, deserialized.A, "abc")
+}