diff --git a/mock/mock.go b/mock/mock.go
index e2e6a2d..5d445c6 100644
--- a/mock/mock.go
+++ b/mock/mock.go
@@ -221,6 +221,14 @@ type Mock struct {
 	mutex sync.Mutex
 }
 
+// String provides a %v format string for Mock.
+// Note: this is used implicitly by Arguments.Diff if a Mock is passed.
+// It exists because go's default %v formatting traverses the struct
+// without acquiring the mutex, which is detected by go test -race.
+func (m *Mock) String() string {
+	return fmt.Sprintf("%[1]T<%[1]p>", m)
+}
+
 // TestData holds any data that might be useful for testing.  Testify ignores
 // this data completely allowing you to do whatever you like with it.
 func (m *Mock) TestData() objx.Map {
diff --git a/mock/mock_test.go b/mock/mock_test.go
index 2b6e704..097addc 100644
--- a/mock/mock_test.go
+++ b/mock/mock_test.go
@@ -1653,3 +1653,40 @@ func unexpectedCallRegex(method, calledArg, expectedArg, diff string) string {
 func ConcurrencyTestMethod(m *Mock) {
 	m.Called()
 }
+
+func TestConcurrentArgumentRead(t *testing.T) {
+	methodUnderTest := func(c caller, u user) {
+		go u.Use(c)
+		c.Call()
+	}
+
+	c := &mockCaller{}
+	defer c.AssertExpectations(t)
+
+	u := &mockUser{}
+	defer u.AssertExpectations(t)
+
+	done := make(chan struct{})
+
+	c.On("Call").Return().Once()
+	u.On("Use", c).Return().Once().Run(func(args Arguments) { close(done) })
+
+	methodUnderTest(c, u)
+	<-done // wait until Use is called or assertions will fail
+}
+
+type caller interface {
+	Call()
+}
+
+type mockCaller struct{ Mock }
+
+func (m *mockCaller) Call() { m.Called() }
+
+type user interface {
+	Use(caller)
+}
+
+type mockUser struct{ Mock }
+
+func (m *mockUser) Use(c caller) { m.Called(c) }