diff --git a/moshi/src/main/java/com/squareup/moshi/JsonReader.java b/moshi/src/main/java/com/squareup/moshi/JsonReader.java
index b42f36f..116eea6 100644
--- a/moshi/src/main/java/com/squareup/moshi/JsonReader.java
+++ b/moshi/src/main/java/com/squareup/moshi/JsonReader.java
@@ -21,6 +21,7 @@ import java.io.IOException;
 import okio.Buffer;
 import okio.BufferedSource;
 import okio.ByteString;
+import okio.Okio;
 import okio.Source;
 
 /**
@@ -263,13 +264,15 @@ public class JsonReader implements Closeable {
   private int[] pathIndices = new int[32];
 
   /**
-   * Creates a new instance that reads a JSON-encoded stream from {@code in}.
+   * Creates a new instance that reads a JSON-encoded stream from {@code source}.
    */
   public JsonReader(Source source) {
     if (source == null) {
       throw new NullPointerException("source == null");
     }
-    throw new UnsupportedOperationException("TODO");
+    BufferedSource bufferedSource = Okio.buffer(source);
+    this.source = bufferedSource;
+    this.buffer = bufferedSource.buffer();
   }
 
   /**
diff --git a/moshi/src/test/java/com/squareup/moshi/JsonReaderTest.java b/moshi/src/test/java/com/squareup/moshi/JsonReaderTest.java
index f971889..966270d 100644
--- a/moshi/src/test/java/com/squareup/moshi/JsonReaderTest.java
+++ b/moshi/src/test/java/com/squareup/moshi/JsonReaderTest.java
@@ -18,6 +18,8 @@ package com.squareup.moshi;
 import java.io.EOFException;
 import java.io.IOException;
 import java.util.Arrays;
+import okio.Buffer;
+import okio.ForwardingSource;
 import okio.Source;
 import org.junit.Ignore;
 import org.junit.Test;
@@ -66,6 +68,31 @@ public final class JsonReaderTest {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
+  @Test public void readObjectBuffer() throws IOException {
+    Buffer buffer = new Buffer().writeUtf8("{\"a\": \"android\", \"b\": \"banana\"}");
+    JsonReader reader = new JsonReader(buffer);
+    reader.beginObject();
+    assertEquals("a", reader.nextName());
+    assertEquals("android", reader.nextString());
+    assertEquals("b", reader.nextName());
+    assertEquals("banana", reader.nextString());
+    reader.endObject();
+    assertEquals(JsonToken.END_DOCUMENT, reader.peek());
+  }
+
+  @Test public void readObjectSource() throws IOException {
+    Buffer buffer = new Buffer().writeUtf8("{\"a\": \"android\", \"b\": \"banana\"}");
+    Source source = new ForwardingSource(buffer) {}; // Mask the Buffer as an unbuffered Source.
+    JsonReader reader = new JsonReader(source);
+    reader.beginObject();
+    assertEquals("a", reader.nextName());
+    assertEquals("android", reader.nextString());
+    assertEquals("b", reader.nextName());
+    assertEquals("banana", reader.nextString());
+    reader.endObject();
+    assertEquals(JsonToken.END_DOCUMENT, reader.peek());
+  }
+
   @Test public void readEmptyObject() throws IOException {
     JsonReader reader = new JsonReader("{}");
     reader.beginObject();