diff --git a/example_test.go b/example_test.go
index c1fc13e..7d0e286 100644
--- a/example_test.go
+++ b/example_test.go
@@ -195,7 +195,7 @@ func Example_stackTrace() {
 func ExampleCause_printf() {
 	err := errors.Wrap(func() error {
 		return func() error {
-			return errors.Errorf("hello %s", fmt.Sprintf("world"))
+			return errors.New("hello world")
 		}()
 	}(), "failed")
 
diff --git a/stack_test.go b/stack_test.go
index 1acd719..aa10a72 100644
--- a/stack_test.go
+++ b/stack_test.go
@@ -142,7 +142,7 @@ func TestStackTrace(t *testing.T) {
 	}, {
 		Cause(func() error {
 			return func() error {
-				return Errorf("hello %s", fmt.Sprintf("world"))
+				return Errorf("hello %s", fmt.Sprintf("world: %s", "ooh"))
 			}()
 		}()), []string{
 			`github.com/pkg/errors.TestStackTrace.func2.1` +