diff --git a/extras/src/main/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactory.java b/extras/src/main/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactory.java
index 3e8aebcf60..a8c6368c28 100644
--- a/extras/src/main/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactory.java
+++ b/extras/src/main/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactory.java
@@ -16,10 +16,6 @@
 
 package com.google.gson.typeadapters;
 
-import java.io.IOException;
-import java.util.LinkedHashMap;
-import java.util.Map;
-
 import com.google.gson.Gson;
 import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
@@ -30,6 +26,10 @@
 import com.google.gson.reflect.TypeToken;
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonWriter;
+import java.io.IOException;
+import java.util.LinkedHashMap;
+import java.util.Map;
+
 
 /**
  * Adapts values whose runtime type may differ from their declaration type. This
@@ -205,7 +205,7 @@ public RuntimeTypeAdapterFactory<T> registerSubtype(Class<? extends T> type) {
 
   @Override
   public <R> TypeAdapter<R> create(Gson gson, TypeToken<R> type) {
-    if (type.getRawType() != baseType) {
+    if (type == null || !baseType.isAssignableFrom(type.getRawType())) {
       return null;
     }
 
diff --git a/extras/src/test/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactoryTest.java b/extras/src/test/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactoryTest.java
index 8c62bef7f4..e58ee0f9c3 100644
--- a/extras/src/test/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactoryTest.java
+++ b/extras/src/test/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactoryTest.java
@@ -34,7 +34,9 @@ public void testRuntimeTypeAdapter() {
 
     CreditCard original = new CreditCard("Jesse", 234);
     assertEquals("{\"type\":\"CreditCard\",\"cvv\":234,\"ownerName\":\"Jesse\"}",
-        gson.toJson(original, BillingInstrument.class));
+        //do not give the explicit typeOfSrc, because if this would be in a list
+        //or an attribute, there would also be no hint. See #712
+        gson.toJson(original));
     BillingInstrument deserialized = gson.fromJson(
         "{type:'CreditCard',cvv:234,ownerName:'Jesse'}", BillingInstrument.class);
     assertEquals("Jesse", deserialized.ownerName);