2 files changed, 18 insertions, 0 deletions
diff --git a/src/encoding/json/encode.go b/src/encoding/json/encode.go
index 07d3098f1c..f085b5a08d 100644
--- a/src/encoding/json/encode.go
+++ b/src/encoding/json/encode.go
@@ -932,6 +932,9 @@ func (w *reflectWithString) resolve() error {
 		return nil
 	}
 	if tm, ok := w.v.Interface().(encoding.TextMarshaler); ok {
+		if w.v.Kind() == reflect.Ptr && w.v.IsNil() {
+			return nil
+		}
 		buf, err := tm.MarshalText()
 		w.s = string(buf)
 		return err
diff --git a/src/encoding/json/encode_test.go b/src/encoding/json/encode_test.go
index bdf2a9f079..642f397fb9 100644
--- a/src/encoding/json/encode_test.go
+++ b/src/encoding/json/encode_test.go
@@ -793,6 +793,21 @@ func TestTextMarshalerMapKeysAreSorted(t *testing.T) {
 	}
 }
 
+// https://golang.org/issue/33675
+func TestNilMarshalerTextMapKey(t *testing.T) {
+	b, err := Marshal(map[*unmarshalerText]int{
+		(*unmarshalerText)(nil):    1,
+		&unmarshalerText{"A", "B"}: 2,
+	})
+	if err != nil {
+		t.Fatalf("Failed to Marshal *text.Marshaler: %v", err)
+	}
+	const want = `{"":1,"A:B":2}`
+	if string(b) != want {
+		t.Errorf("Marshal map with *text.Marshaler keys: got %#q, want %#q", b, want)
+	}
+}
+
 var re = regexp.MustCompile
 
 // syntactic checks on form of marshaled floating point numbers.