diff --git a/okhttp/src/main/java/com/squareup/okhttp/internal/okio/ByteString.java b/okhttp/src/main/java/com/squareup/okhttp/internal/okio/ByteString.java
index 0721caeea..2397aabcb 100644
--- a/okhttp/src/main/java/com/squareup/okhttp/internal/okio/ByteString.java
+++ b/okhttp/src/main/java/com/squareup/okhttp/internal/okio/ByteString.java
@@ -19,6 +19,7 @@ import java.io.EOFException;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
+import java.io.UnsupportedEncodingException;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 import java.util.Arrays;
@@ -58,16 +59,24 @@ public final class ByteString {
 
   /** Returns a new byte string containing the {@code UTF-8} bytes of {@code s}. */
   public static ByteString encodeUtf8(String s) {
-    ByteString byteString = new ByteString(s.getBytes(Util.UTF_8));
-    byteString.utf8 = s;
-    return byteString;
+    try {
+      ByteString byteString = new ByteString(s.getBytes(Util.UTF_8));
+      byteString.utf8 = s;
+      return byteString;
+    } catch (UnsupportedEncodingException e) {
+      throw new AssertionError(e);
+    }
   }
 
   /** Constructs a new {@code String} by decoding the bytes as {@code UTF-8}. */
   public String utf8() {
     String result = utf8;
     // We don't care if we double-allocate in racy code.
-    return result != null ? result : (utf8 = new String(data, Util.UTF_8));
+    try {
+      return result != null ? result : (utf8 = new String(data, Util.UTF_8));
+    } catch (UnsupportedEncodingException e) {
+      throw new AssertionError(e);
+    }
   }
 
   /**
diff --git a/okhttp/src/main/java/com/squareup/okhttp/internal/okio/InflaterSource.java b/okhttp/src/main/java/com/squareup/okhttp/internal/okio/InflaterSource.java
index aa6f5ba5d..91dcb90af 100644
--- a/okhttp/src/main/java/com/squareup/okhttp/internal/okio/InflaterSource.java
+++ b/okhttp/src/main/java/com/squareup/okhttp/internal/okio/InflaterSource.java
@@ -76,7 +76,9 @@ public final class InflaterSource implements Source {
         }
         if (sourceExhausted) throw new EOFException("source exhausted prematurely");
       } catch (DataFormatException e) {
-        throw new IOException(e);
+        IOException io = new IOException();
+        io.initCause(e);
+        throw io;
       }
     }
   }
diff --git a/okhttp/src/main/java/com/squareup/okhttp/internal/okio/OkBuffer.java b/okhttp/src/main/java/com/squareup/okhttp/internal/okio/OkBuffer.java
index 6e0b5ff6e..2b2949f6a 100644
--- a/okhttp/src/main/java/com/squareup/okhttp/internal/okio/OkBuffer.java
+++ b/okhttp/src/main/java/com/squareup/okhttp/internal/okio/OkBuffer.java
@@ -18,6 +18,7 @@ package com.squareup.okhttp.internal.okio;
 import java.io.EOFException;
 import java.io.InputStream;
 import java.io.OutputStream;
+import java.io.UnsupportedEncodingException;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 import java.util.ArrayList;
@@ -253,19 +254,27 @@ public final class OkBuffer implements BufferedSource, BufferedSink, Cloneable {
     Segment head = this.head;
     if (head.pos + byteCount > head.limit) {
       // If the string spans multiple segments, delegate to readBytes().
-      return new String(readBytes(byteCount), UTF_8);
+      try {
+        return new String(readBytes(byteCount), UTF_8);
+      } catch (UnsupportedEncodingException e) {
+        throw new AssertionError(e);
+      }
     }
 
-    String result = new String(head.data, head.pos, (int) byteCount, UTF_8);
-    head.pos += byteCount;
-    this.size -= byteCount;
+    try {
+      String result = new String(head.data, head.pos, (int) byteCount, UTF_8);
+      head.pos += byteCount;
+      this.size -= byteCount;
 
-    if (head.pos == head.limit) {
-      this.head = head.pop();
-      SegmentPool.INSTANCE.recycle(head);
+      if (head.pos == head.limit) {
+        this.head = head.pop();
+        SegmentPool.INSTANCE.recycle(head);
+      }
+
+      return result;
+    } catch (UnsupportedEncodingException e) {
+      throw new AssertionError(e);
     }
-
-    return result;
   }
 
   @Override public String readUtf8Line(boolean throwOnEof) throws EOFException {
@@ -369,8 +378,12 @@ public final class OkBuffer implements BufferedSource, BufferedSink, Cloneable {
 
   /** Encodes {@code string} as UTF-8 and appends the bytes to this. */
   @Override public OkBuffer writeUtf8(String string) {
-    byte[] data = string.getBytes(UTF_8);
-    return write(data, 0, data.length);
+    try {
+      byte[] data = string.getBytes(UTF_8);
+      return write(data, 0, data.length);
+    } catch (UnsupportedEncodingException e) {
+      throw new AssertionError(e);
+    }
   }
 
   @Override public OkBuffer write(byte[] source) {
diff --git a/okhttp/src/main/java/com/squareup/okhttp/internal/okio/Util.java b/okhttp/src/main/java/com/squareup/okhttp/internal/okio/Util.java
index a626c343b..d3a60e9eb 100644
--- a/okhttp/src/main/java/com/squareup/okhttp/internal/okio/Util.java
+++ b/okhttp/src/main/java/com/squareup/okhttp/internal/okio/Util.java
@@ -15,11 +15,10 @@
  */
 package com.squareup.okhttp.internal.okio;
 
-import java.nio.charset.Charset;
 
 final class Util {
   /** A cheap and type-safe constant for the UTF-8 Charset. */
-  public static final Charset UTF_8 = Charset.forName("UTF-8");
+  public static final String UTF_8 = "UTF-8";
 
   private Util() {
   }