diff --git a/deep.go b/deep.go
index 254ee7d..3e6636c 100644
--- a/deep.go
+++ b/deep.go
@@ -27,7 +27,9 @@ var (
 	LogErrors = false
 
 	// CompareUnexportedFields causes unexported struct fields, like s in
-	// T{s int}, to be compared when true.
+	// T{s int}, to be compared when true. This does not work for comparing
+	// error or Time types on unexported fields because methods on unexported
+	// fields cannot be called.
 	CompareUnexportedFields = false
 
 	// NilSlicesAreEmpty causes a nil slice to be equal to an empty slice.
diff --git a/deep_test.go b/deep_test.go
index d2ae7ce..98fba1f 100644
--- a/deep_test.go
+++ b/deep_test.go
@@ -1408,7 +1408,9 @@ func TestErrorUnexported(t *testing.T) {
 	type foo struct {
 		bar error
 	}
+	defaultCompareUnexportedFields := deep.CompareUnexportedFields
 	deep.CompareUnexportedFields = true
+	defer func() { deep.CompareUnexportedFields = defaultCompareUnexportedFields }()
 	e1 := foo{bar: fmt.Errorf("error")}
 	e2 := foo{bar: fmt.Errorf("error")}
 	deep.Equal(e1, e2)