diff --git a/gerrit-httpd/src/main/java/com/google/gerrit/httpd/restapi/RestApiServlet.java b/gerrit-httpd/src/main/java/com/google/gerrit/httpd/restapi/RestApiServlet.java
index 5a0956dcdd..a7b53cfcc8 100644
--- a/gerrit-httpd/src/main/java/com/google/gerrit/httpd/restapi/RestApiServlet.java
+++ b/gerrit-httpd/src/main/java/com/google/gerrit/httpd/restapi/RestApiServlet.java
@@ -105,6 +105,7 @@ import org.slf4j.LoggerFactory;
 import java.io.BufferedReader;
 import java.io.BufferedWriter;
 import java.io.EOFException;
+import java.io.FilterOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
@@ -767,10 +768,15 @@ public class RestApiServlet extends HttpServlet {
       b64 = new BinaryResult() {
         @Override
         public void writeTo(OutputStream out) throws IOException {
-          try (OutputStreamWriter w = new OutputStreamWriter(out, ISO_8859_1);
+          try (OutputStreamWriter w = new OutputStreamWriter(
+                new FilterOutputStream(out) {
+                  @Override
+                  public void close() {
+                    // Do not close out, but only w and e.
+                  }
+                }, ISO_8859_1);
               OutputStream e = BaseEncoding.base64().encodingStream(w)) {
             src.writeTo(e);
-            e.flush();
           }
         }
       };