diff --git a/src/HttpHeader.cc b/src/HttpHeader.cc
index 8513cb56..1bba0ad2 100644
--- a/src/HttpHeader.cc
+++ b/src/HttpHeader.cc
@@ -293,4 +293,28 @@ const std::string& HttpHeader::getRequestPath() const
   return requestPath_;
 }
 
+bool HttpHeader::fieldContains(const std::string& name,
+                               const std::string& value)
+{
+  std::pair<std::multimap<std::string, std::string>::const_iterator,
+            std::multimap<std::string, std::string>::const_iterator> range =
+    equalRange(name);
+  for(std::multimap<std::string, std::string>::const_iterator i = range.first;
+      i != range.second; ++i) {
+    std::vector<Scip> values;
+    util::splitIter((*i).second.begin(), (*i).second.end(),
+                    std::back_inserter(values),
+                    ',',
+                    true // doStrip
+                    );
+    for(std::vector<Scip>::const_iterator j = values.begin(),
+          eoj = values.end(); j != eoj; ++j) {
+      if(util::strieq((*j).first, (*j).second, value.begin(), value.end())) {
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
 } // namespace aria2
diff --git a/src/HttpHeader.h b/src/HttpHeader.h
index b337e089..8791a4c5 100644
--- a/src/HttpHeader.h
+++ b/src/HttpHeader.h
@@ -66,6 +66,7 @@ public:
   HttpHeader();
   ~HttpHeader();
 
+  // For all methods, use lowercased header field name.
   void put(const std::string& name, const std::string& value);
   bool defined(const std::string& name) const;
   const std::string& find(const std::string& name) const;
@@ -121,6 +122,10 @@ public:
   // Clears table_. responseStatus_ and version_ are unchanged.
   void clearField();
 
+  // Returns true if heder field |name| contains |value|. This method
+  // assumes the values of the header field is delimited by ','.
+  bool fieldContains(const std::string& name, const std::string& value);
+
   static const std::string LOCATION;
   static const std::string TRANSFER_ENCODING;
   static const std::string CONTENT_ENCODING;
diff --git a/src/HttpServerCommand.cc b/src/HttpServerCommand.cc
index 026c2627..0e13094e 100644
--- a/src/HttpServerCommand.cc
+++ b/src/HttpServerCommand.cc
@@ -174,10 +174,8 @@ bool HttpServerCommand::execute()
         e_->setNoWait(true);
         return true;
       }
-      const std::string& upgradeHd = header->find("upgrade");
-      const std::string& connectionHd = header->find("connection");
-      if(util::strieq(upgradeHd.begin(), upgradeHd.end(), "websocket") &&
-         util::strieq(connectionHd.begin(), connectionHd.end(), "upgrade")) {
+      if(header->fieldContains("upgrade", "websocket") &&
+         header->fieldContains("connection", "upgrade")) {
 #ifdef ENABLE_WEBSOCKET
         int status = websocketHandshake(header);
         Command* command;
diff --git a/test/HttpHeaderTest.cc b/test/HttpHeaderTest.cc
index 690f3818..f1add642 100644
--- a/test/HttpHeaderTest.cc
+++ b/test/HttpHeaderTest.cc
@@ -14,6 +14,7 @@ class HttpHeaderTest:public CppUnit::TestFixture {
   CPPUNIT_TEST(testFindAll);
   CPPUNIT_TEST(testClearField);
   CPPUNIT_TEST(testFill);
+  CPPUNIT_TEST(testFieldContains);
   CPPUNIT_TEST_SUITE_END();
   
 public:
@@ -21,6 +22,7 @@ public:
   void testFindAll();
   void testClearField();
   void testFill();
+  void testFieldContains();
 };
 
 
@@ -175,4 +177,21 @@ void HttpHeaderTest::testFill()
                        h.findAll("duplicate")[1]);
 }
 
+void HttpHeaderTest::testFieldContains()
+{
+  HttpHeader h;
+  h.put("connection", "Keep-Alive, Upgrade");
+  h.put("upgrade", "WebSocket");
+  h.put("sec-websocket-version", "13");
+  h.put("sec-websocket-version", "8, 7");
+  CPPUNIT_ASSERT(h.fieldContains("connection", "upgrade"));
+  CPPUNIT_ASSERT(h.fieldContains("connection", "keep-alive"));
+  CPPUNIT_ASSERT(!h.fieldContains("connection", "close"));
+  CPPUNIT_ASSERT(h.fieldContains("upgrade", "websocket"));
+  CPPUNIT_ASSERT(!h.fieldContains("upgrade", "spdy"));
+  CPPUNIT_ASSERT(h.fieldContains("sec-websocket-version", "13"));
+  CPPUNIT_ASSERT(h.fieldContains("sec-websocket-version", "8"));
+  CPPUNIT_ASSERT(!h.fieldContains("sec-websocket-version", "6"));
+}
+
 } // namespace aria2