diff --git a/.gitignore b/.gitignore
index 2a866d88..40776a14 100644
--- a/.gitignore
+++ b/.gitignore
@@ -17,3 +17,6 @@ mockgen/mockgen
 # Editors
 .vscode
 .idea
+
+# vendor directory used for IDEs
+/vendor
diff --git a/mockgen/internal/tests/mock_in_test_package/mock_test.go b/mockgen/internal/tests/mock_in_test_package/mock_test.go
index f17a49ed..08bc27b0 100644
--- a/mockgen/internal/tests/mock_in_test_package/mock_test.go
+++ b/mockgen/internal/tests/mock_in_test_package/mock_test.go
@@ -8,7 +8,7 @@ import (
 	reflect "reflect"
 
 	gomock "github.com/golang/mock/gomock"
-	mock_in_test_package "github.com/golang/mock/mockgen/internal/tests/mock_in_test_package"
+	users "github.com/golang/mock/mockgen/internal/tests/mock_in_test_package"
 )
 
 // MockFinder is a mock of Finder interface.
@@ -35,7 +35,7 @@ func (m *MockFinder) EXPECT() *MockFinderMockRecorder {
 }
 
 // Add mocks base method.
-func (m *MockFinder) Add(u mock_in_test_package.User) {
+func (m *MockFinder) Add(u users.User) {
 	m.ctrl.T.Helper()
 	m.ctrl.Call(m, "Add", u)
 }
@@ -47,10 +47,10 @@ func (mr *MockFinderMockRecorder) Add(u interface{}) *gomock.Call {
 }
 
 // FindUser mocks base method.
-func (m *MockFinder) FindUser(name string) mock_in_test_package.User {
+func (m *MockFinder) FindUser(name string) users.User {
 	m.ctrl.T.Helper()
 	ret := m.ctrl.Call(m, "FindUser", name)
-	ret0, _ := ret[0].(mock_in_test_package.User)
+	ret0, _ := ret[0].(users.User)
 	return ret0
 }
 
diff --git a/mockgen/mockgen.go b/mockgen/mockgen.go
index 72a1c960..79cb921c 100644
--- a/mockgen/mockgen.go
+++ b/mockgen/mockgen.go
@@ -21,6 +21,7 @@ package main
 import (
 	"bytes"
 	"encoding/json"
+	"errors"
 	"flag"
 	"fmt"
 	"go/token"
@@ -107,19 +108,6 @@ func main() {
 		return
 	}
 
-	dst := os.Stdout
-	if len(*destination) > 0 {
-		if err := os.MkdirAll(filepath.Dir(*destination), os.ModePerm); err != nil {
-			log.Fatalf("Unable to create directory: %v", err)
-		}
-		f, err := os.Create(*destination)
-		if err != nil {
-			log.Fatalf("Failed opening destination file: %v", err)
-		}
-		defer f.Close()
-		dst = f
-	}
-
 	outputPackageName := *packageOut
 	if outputPackageName == "" {
 		// pkg.Name in reflect mode is the base name of the import path,
@@ -171,7 +159,27 @@ func main() {
 	if err := g.Generate(pkg, outputPackageName, outputPackagePath); err != nil {
 		log.Fatalf("Failed generating mock: %v", err)
 	}
-	if _, err := dst.Write(g.Output()); err != nil {
+	output := g.Output()
+	dst := os.Stdout
+	if len(*destination) > 0 {
+		if err := os.MkdirAll(filepath.Dir(*destination), os.ModePerm); err != nil {
+			log.Fatalf("Unable to create directory: %v", err)
+		}
+		existing, err := ioutil.ReadFile(*destination)
+		if err != nil && !errors.Is(err, os.ErrNotExist) {
+			log.Fatalf("Failed reading pre-exiting destination file: %v", err)
+		}
+		if len(existing) == len(output) && bytes.Compare(existing, output) == 0 {
+			return
+		}
+		f, err := os.Create(*destination)
+		if err != nil {
+			log.Fatalf("Failed opening destination file: %v", err)
+		}
+		defer f.Close()
+		dst = f
+	}
+	if _, err := dst.Write(output); err != nil {
 		log.Fatalf("Failed writing to destination: %v", err)
 	}
 }