diff --git a/src/encoding/json/decode_test.go b/src/encoding/json/decode_test.go
index f208ee8a7c..4834c062cc 100644
--- a/src/encoding/json/decode_test.go
+++ b/src/encoding/json/decode_test.go
@@ -1393,3 +1393,27 @@ func TestInvalidUnmarshal(t *testing.T) {
 		}
 	}
 }
+
+// Test that string option is ignored for invalid types.
+// Issue 9812.
+func TestInvalidStringOption(t *testing.T) {
+	num := 0
+	item := struct {
+		T time.Time         `json:",string"`
+		M map[string]string `json:",string"`
+		S []string          `json:",string"`
+		A [1]string         `json:",string"`
+		I interface{}       `json:",string"`
+		P *int              `json:",string"`
+	}{M: make(map[string]string), S: make([]string, 0), I: num, P: &num}
+
+	data, err := Marshal(item)
+	if err != nil {
+		t.Fatalf("Marshal: %v", err)
+	}
+
+	err = Unmarshal(data, &item)
+	if err != nil {
+		t.Fatalf("Unmarshal: %v", err)
+	}
+}
diff --git a/src/encoding/json/encode.go b/src/encoding/json/encode.go
index 08bb67134e..90782deb70 100644
--- a/src/encoding/json/encode.go
+++ b/src/encoding/json/encode.go
@@ -1043,6 +1043,19 @@ func typeFields(t reflect.Type) []field {
 					ft = ft.Elem()
 				}
 
+				// Only strings, floats, integers, and booleans can be quoted.
+				quoted := false
+				if opts.Contains("string") {
+					switch ft.Kind() {
+					case reflect.Bool,
+						reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
+						reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
+						reflect.Float32, reflect.Float64,
+						reflect.String:
+						quoted = true
+					}
+				}
+
 				// Record found field and index sequence.
 				if name != "" || !sf.Anonymous || ft.Kind() != reflect.Struct {
 					tagged := name != ""
@@ -1055,7 +1068,7 @@ func typeFields(t reflect.Type) []field {
 						index:     index,
 						typ:       ft,
 						omitEmpty: opts.Contains("omitempty"),
-						quoted:    opts.Contains("string"),
+						quoted:    quoted,
 					}))
 					if count[f.typ] > 1 {
 						// If there were multiple instances, add a second,