diff --git a/src/encoding/json/decode_test.go b/src/encoding/json/decode_test.go
index fc546bf2a7..27ceee471a 100644
--- a/src/encoding/json/decode_test.go
+++ b/src/encoding/json/decode_test.go
@@ -195,6 +195,11 @@ type embed struct {
 	Q int
 }
 
+type Issue21357 struct {
+	*embed
+	R int
+}
+
 type Loop struct {
 	Loop1 int `json:",omitempty"`
 	Loop2 int `json:",omitempty"`
@@ -866,6 +871,20 @@ var unmarshalTests = []unmarshalTest{
 		err: fmt.Errorf("json: unknown field \"extra\""),
 		disallowUnknownFields: true,
 	},
+
+	// Issue 21357.
+	// Ignore any embedded fields that are pointers to unexported structs.
+	{
+		in:  `{"Q":1,"R":2}`,
+		ptr: new(Issue21357),
+		out: Issue21357{R: 2},
+	},
+	{
+		in:  `{"Q":1,"R":2}`,
+		ptr: new(Issue21357),
+		err: fmt.Errorf("json: unknown field \"Q\""),
+		disallowUnknownFields: true,
+	},
 }
 
 func TestMarshal(t *testing.T) {
diff --git a/src/encoding/json/encode.go b/src/encoding/json/encode.go
index 317a5a940d..66d1a183b0 100644
--- a/src/encoding/json/encode.go
+++ b/src/encoding/json/encode.go
@@ -1094,11 +1094,18 @@ func typeFields(t reflect.Type) []field {
 				isUnexported := sf.PkgPath != ""
 				if sf.Anonymous {
 					t := sf.Type
-					if t.Kind() == reflect.Ptr {
+					isPointer := t.Kind() == reflect.Ptr
+					if isPointer {
 						t = t.Elem()
 					}
-					if isUnexported && t.Kind() != reflect.Struct {
-						// Ignore embedded fields of unexported non-struct types.
+					isStruct := t.Kind() == reflect.Struct
+					if isUnexported && (!isStruct || isPointer) {
+						// Ignore embedded fields of unexported non-struct types
+						// or pointers to unexported struct types.
+						//
+						// The latter is forbidden because unmarshal is unable
+						// to assign a new struct to the unexported field.
+						// See https://golang.org/issue/21357
 						continue
 					}
 					// Do not ignore embedded fields of unexported struct types
diff --git a/src/encoding/json/encode_test.go b/src/encoding/json/encode_test.go
index 0f194e13d2..df7338c98d 100644
--- a/src/encoding/json/encode_test.go
+++ b/src/encoding/json/encode_test.go
@@ -364,8 +364,9 @@ func TestAnonymousFields(t *testing.T) {
 		want: `{"X":2,"Y":4}`,
 	}, {
 		// Exported fields of pointers to embedded structs should have their
-		// exported fields be serialized regardless of whether the struct types
-		// themselves are exported.
+		// exported fields be serialized only for exported struct types.
+		// Pointers to unexported structs are not allowed since the decoder
+		// is unable to allocate a struct for that field
 		label: "EmbeddedStructPointer",
 		makeInput: func() interface{} {
 			type (
@@ -378,7 +379,7 @@ func TestAnonymousFields(t *testing.T) {
 			)
 			return S{&s1{1, 2}, &S2{3, 4}}
 		},
-		want: `{"X":2,"Y":4}`,
+		want: `{"Y":4}`,
 	}, {
 		// Exported fields on embedded unexported structs at multiple levels
 		// of nesting should still be serialized.