diff --git a/mock/mock.go b/mock/mock.go
index 111a281..9895bb5 100644
--- a/mock/mock.go
+++ b/mock/mock.go
@@ -458,6 +458,47 @@ func AnythingOfType(t string) AnythingOfTypeArgument {
 	return AnythingOfTypeArgument(t)
 }
 
+// argumentMatcher performs custom argument matching, returning whether or
+// not the argument is matched by the expectation fixture function.
+type argumentMatcher struct {
+	// fn is a function which accepts one argument, and returns a bool.
+	fn reflect.Value
+}
+
+func (f argumentMatcher) Matches(argument interface{}) bool {
+	expectType := f.fn.Type().In(0)
+
+	if reflect.TypeOf(argument).AssignableTo(expectType) {
+		result := f.fn.Call([]reflect.Value{reflect.ValueOf(argument)})
+		return result[0].Bool()
+	} else {
+		return false
+	}
+}
+
+func (f argumentMatcher) String() string {
+	return fmt.Sprintf("func(%s) bool", f.fn.Type().In(0).Name())
+}
+
+// Builds an argumentMatcher from |fn|, which must be a function accepting a
+// single argument (of any type) which returns a bool. If |fn| doesn't match
+// the required signature, MathedBy() panics.
+func MatchedBy(fn interface{}) argumentMatcher {
+	fnType := reflect.TypeOf(fn)
+
+	if fnType.Kind() != reflect.Func {
+		panic(fmt.Sprintf("assert: arguments: %s is not a func", fn))
+	}
+	if fnType.NumIn() != 1 {
+		panic(fmt.Sprintf("assert: arguments: %s does not take exactly one argument", fn))
+	}
+	if fnType.NumOut() != 1 || fnType.Out(0).Kind() != reflect.Bool {
+		panic(fmt.Sprintf("assert: arguments: %s does not return a bool", fn))
+	}
+
+	return argumentMatcher{fn: reflect.ValueOf(fn)}
+}
+
 // Get Returns the argument at the specified index.
 func (args Arguments) Get(index int) interface{} {
 	if index+1 > len(args) {
@@ -505,7 +546,14 @@ func (args Arguments) Diff(objects []interface{}) (string, int) {
 			expected = args[i]
 		}
 
-		if reflect.TypeOf(expected) == reflect.TypeOf((*AnythingOfTypeArgument)(nil)).Elem() {
+		if matcher, ok := expected.(argumentMatcher); ok {
+			if matcher.Matches(actual) {
+				output = fmt.Sprintf("%s\t%d: \u2705  %s matched by %s\n", output, i, actual, matcher)
+			} else {
+				differences++
+				output = fmt.Sprintf("%s\t%d: \u2705  %s not matched by %s\n", output, i, actual, matcher)
+			}
+		} else if reflect.TypeOf(expected) == reflect.TypeOf((*AnythingOfTypeArgument)(nil)).Elem() {
 
 			// type checking
 			if reflect.TypeOf(actual).Name() != string(expected.(AnythingOfTypeArgument)) && reflect.TypeOf(actual).String() != string(expected.(AnythingOfTypeArgument)) {
diff --git a/mock/mock_test.go b/mock/mock_test.go
index 1315cec..f6bde46 100644
--- a/mock/mock_test.go
+++ b/mock/mock_test.go
@@ -147,6 +147,63 @@ func Test_Mock_On_WithFuncArg(t *testing.T) {
 	})
 }
 
+func Test_Mock_On_WithIntArgMatcher(t *testing.T) {
+	var mockedService TestExampleImplementation
+
+	mockedService.On("TheExampleMethod",
+		MatchedBy(func(a int) bool {
+			return a == 1
+		}), MatchedBy(func(b int) bool {
+			return b == 2
+		}), MatchedBy(func(c int) bool {
+			return c == 3
+		})).Return(0, nil)
+
+	assert.Panics(t, func() {
+		mockedService.TheExampleMethod(1, 2, 4)
+	})
+	assert.Panics(t, func() {
+		mockedService.TheExampleMethod(2, 2, 3)
+	})
+	assert.NotPanics(t, func() {
+		mockedService.TheExampleMethod(1, 2, 3)
+	})
+}
+
+func Test_Mock_On_WithPtrArgMatcher(t *testing.T) {
+	var mockedService TestExampleImplementation
+
+	mockedService.On("TheExampleMethod3",
+		MatchedBy(func(a *ExampleType) bool { return a.ran == true }),
+	).Return(nil)
+
+	mockedService.On("TheExampleMethod3",
+		MatchedBy(func(a *ExampleType) bool { return a.ran == false }),
+	).Return(errors.New("error!"))
+
+	assert.Equal(t, mockedService.TheExampleMethod3(&ExampleType{true}), nil)
+	assert.EqualError(t, mockedService.TheExampleMethod3(&ExampleType{false}), "error!")
+}
+
+func Test_Mock_On_WithFuncArgMatcher(t *testing.T) {
+	var mockedService TestExampleImplementation
+
+	fixture1, fixture2 := errors.New("fixture1"), errors.New("fixture2")
+
+	mockedService.On("TheExampleMethodFunc",
+		MatchedBy(func(a func(string) error) bool { return a("string") == fixture1 }),
+	).Return(errors.New("fixture1"))
+
+	mockedService.On("TheExampleMethodFunc",
+		MatchedBy(func(a func(string) error) bool { return a("string") == fixture2 }),
+	).Return(errors.New("fixture2"))
+
+	assert.EqualError(t, mockedService.TheExampleMethodFunc(
+		func(string) error { return fixture1 }), "fixture1")
+	assert.EqualError(t, mockedService.TheExampleMethodFunc(
+		func(string) error { return fixture2 }), "fixture2")
+}
+
 func Test_Mock_On_WithVariadicFunc(t *testing.T) {
 
 	// make a test impl object
@@ -937,6 +994,28 @@ func Test_Arguments_Diff_WithAnythingOfTypeArgument_Failing(t *testing.T) {
 
 }
 
+func Test_Arguments_Diff_WithArgMatcher(t *testing.T) {
+	matchFn := func(a int) bool {
+		return a == 123
+	}
+	var args Arguments = []interface{}{"string", MatchedBy(matchFn), true}
+
+	diff, count := args.Diff([]interface{}{"string", 124, true})
+	assert.Equal(t, 1, count)
+	assert.Contains(t, diff, `%!s(int=124) not matched by func(int) bool`)
+
+	diff, count = args.Diff([]interface{}{"string", false, true})
+	assert.Equal(t, 1, count)
+	assert.Contains(t, diff, `%!s(bool=false) not matched by func(int) bool`)
+
+	diff, count = args.Diff([]interface{}{"string", 123, false})
+	assert.Contains(t, diff, `%!s(int=123) matched by func(int) bool`)
+
+	diff, count = args.Diff([]interface{}{"string", 123, true})
+	assert.Equal(t, 0, count)
+	assert.Contains(t, diff, `No differences.`)
+}
+
 func Test_Arguments_Assert(t *testing.T) {
 
 	var args Arguments = []interface{}{"string", 123, true}