diff --git a/problem-gson/src/main/java/org/zalando/problem/gson/DefaultProblemAdapter.java b/problem-gson/src/main/java/org/zalando/problem/gson/DefaultProblemAdapter.java
index aa9dd9d..0593d8a 100644
--- a/problem-gson/src/main/java/org/zalando/problem/gson/DefaultProblemAdapter.java
+++ b/problem-gson/src/main/java/org/zalando/problem/gson/DefaultProblemAdapter.java
@@ -36,7 +36,7 @@ final class DefaultProblemAdapter extends TypeAdapter<ThrowableProblem> {
                 gson,
                 stackTraces,
                 gson.getAdapter(String.class),
-                URITypeAdapter.TYPE,
+                gson.getAdapter(URI.class),
                 gson.getAdapter(new TypeToken<Map<String, Object>>() {
                     // nothing to do here
                 }),
@@ -48,7 +48,7 @@ final class DefaultProblemAdapter extends TypeAdapter<ThrowableProblem> {
     public void write(final JsonWriter out, final ThrowableProblem problem) throws IOException {
         final JsonObject object = new JsonObject();
 
-        object.add("type", uriAdapter.toJsonTree(problem.getType()));
+        object.add("type", URITypeAdapter.TYPE.toJsonTree(problem.getType()));
         object.add("title", stringAdapter.toJsonTree(problem.getTitle()));
         object.add("status", status.toJsonTree(problem.getStatus()));
         object.add("detail", stringAdapter.toJsonTree(problem.getDetail()));
@@ -78,7 +78,7 @@ public ThrowableProblem read(final JsonReader in) throws IOException {
             final String name = in.nextName();
             switch (name) {
                 case "type":
-                    builder.withType(uriAdapter.read(in));
+                    builder.withType(URITypeAdapter.TYPE.read(in));
                     break;
                 case "title":
                     builder.withTitle(stringAdapter.read(in));
diff --git a/problem-gson/src/test/java/org/zalando/problem/gson/GsonProblemTest.java b/problem-gson/src/test/java/org/zalando/problem/gson/GsonProblemTest.java
index 82b2636..31e4ee8 100644
--- a/problem-gson/src/test/java/org/zalando/problem/gson/GsonProblemTest.java
+++ b/problem-gson/src/test/java/org/zalando/problem/gson/GsonProblemTest.java
@@ -83,6 +83,52 @@ void shouldSerializeCustomProperties() {
                 .assertThat("$.product", is("B00027Y5QG"));
     }
 
+    @Test
+    void shouldPreserveNullInstance() {
+        final Problem problem = gson.fromJson("{\"instance\":null}", Problem.class);
+
+        assertThat(problem.getInstance(), is(nullValue()));
+        assertThat(problem.getType(), is(Problem.DEFAULT_TYPE));
+    }
+
+    @Test
+    void shouldRoundTripNullInstance() {
+        final Gson gson = new GsonBuilder()
+                .registerTypeAdapterFactory(new ProblemAdapterFactory())
+                .serializeNulls()
+                .create();
+        final Problem problem = Problem.valueOf(BAD_REQUEST);
+
+        final Problem copy = gson.fromJson(gson.toJson(problem), Problem.class);
+
+        assertThat(copy.getInstance(), is(nullValue()));
+        assertThat(copy.getType(), is(Problem.DEFAULT_TYPE));
+    }
+
+    @Test
+    void shouldPreserveAboutBlankInstance() {
+        final Problem problem = Problem.builder()
+                .withInstance(URI.create("about:blank"))
+                .build();
+
+        final String json = gson.toJson(problem);
+
+        with(json).assertThat("$.instance", is("about:blank"));
+        assertThat(gson.fromJson(json, Problem.class).getInstance(), is(problem.getInstance()));
+    }
+
+    @Test
+    void shouldRoundTripRelativeInstance() {
+        final Problem problem = Problem.builder()
+                .withInstance(URI.create("/problems/123"))
+                .build();
+
+        final String json = gson.toJson(problem);
+
+        with(json).assertThat("$.instance", is("/problems/123"));
+        assertThat(gson.fromJson(json, Problem.class).getInstance(), is(problem.getInstance()));
+    }
+
     @Test
     void shouldSerializeCustomProblem() {
         final int balance = 10;