diff --git a/.travis.yml b/.travis.yml
index 8978a8e0..0d5661c1 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,4 +1,4 @@
-language: c
+language: c++
 sudo: false
 addons:
   apt:
@@ -7,16 +7,19 @@ addons:
     packages:
     - g++-4.8
 env:
-- ARDUINO_VERSION=1.6.8 ARDUINO_ESP8266_VERSION=2.1.0 GCC_VERSION=4.8 ARDUINO_ROOT=${HOME}/arduino-${ARDUINO_VERSION} ARDUINO_ESP8266_ROOT=${ARDUINO_ROOT}/hardware/esp8266com/esp8266 ARDUINO_HOME=${HOME}/Arduino CXX=g++-${GCC_VERSION}
-- ARDUINO_VERSION=1.6.8 ARDUINO_ESP8266_VERSION=2.2.0-rc1 GCC_VERSION=4.8 ARDUINO_ROOT=${HOME}/arduino-${ARDUINO_VERSION} ARDUINO_ESP8266_ROOT=${ARDUINO_ROOT}/hardware/esp8266com/esp8266 ARDUINO_HOME=${HOME}/Arduino CXX=g++-${GCC_VERSION}
-- ARDUINO_VERSION=nightly ARDUINO_ESP8266_VERSION=master GCC_VERSION=4.8 ARDUINO_ROOT=${HOME}/arduino-${ARDUINO_VERSION} ARDUINO_ESP8266_ROOT=${ARDUINO_ROOT}/hardware/esp8266com/esp8266 ARDUINO_HOME=${HOME}/Arduino CXX=g++-${GCC_VERSION}
+- ARDUINO_VERSION=1.6.8 ARDUINO_ESP8266_VERSION=2.1.0 ARDUINO_ROOT=${HOME}/arduino-${ARDUINO_VERSION} ARDUINO_ESP8266_ROOT=${ARDUINO_ROOT}/hardware/esp8266com/esp8266 ARDUINO_HOME=${HOME}/Arduino
+- ARDUINO_VERSION=1.6.8 ARDUINO_ESP8266_VERSION=2.2.0-rc1 ARDUINO_ROOT=${HOME}/arduino-${ARDUINO_VERSION} ARDUINO_ESP8266_ROOT=${ARDUINO_ROOT}/hardware/esp8266com/esp8266 ARDUINO_HOME=${HOME}/Arduino
+- ARDUINO_VERSION=nightly ARDUINO_ESP8266_VERSION=master ARDUINO_ROOT=${HOME}/arduino-${ARDUINO_VERSION} ARDUINO_ESP8266_ROOT=${ARDUINO_ROOT}/hardware/esp8266com/esp8266 ARDUINO_HOME=${HOME}/Arduino
 install:
+- if [ "$CXX" = "g++" ]; then export CXX="g++-4.8" CC="gcc-4.8"; fi
 - ( cd ${HOME} && curl -O https://downloads.arduino.cc/arduino-${ARDUINO_VERSION}-linux64.tar.xz && tar xvf arduino-${ARDUINO_VERSION}-linux64.tar.xz )
 - git clone --branch ${ARDUINO_ESP8266_VERSION} https://github.com/esp8266/Arduino.git ${ARDUINO_ESP8266_ROOT}
+- git submodule init && git submodule update
 - ( cd ${ARDUINO_ESP8266_ROOT}/tools && python get.py )
 before_script:
 - mkdir -p ${ARDUINO_HOME}/libraries
 - ( cd ${ARDUINO_HOME}/libraries && ln -s ${TRAVIS_BUILD_DIR} firebase-arduino && ln -s ${TRAVIS_BUILD_DIR}/src/third-party/arduino-json-5.2 ArduinoJson )
 script:
 - ${ARDUINO_ROOT}/arduino-builder -verbose  -hardware ${ARDUINO_ROOT}/hardware/ -tools ${ARDUINO_ESP8266_ROOT}/tools/ -tools ${ARDUINO_ROOT}/tools-builder/ -fqbn esp8266com:esp8266:nodemcuv2 -libraries ${ARDUINO_HOME}/libraries/ -prefs build.flash_ld=${ARDUINO_ESP8266_ROOT}/tools/sdk/ld/eagle.flash.4m.ld -prefs build.flash_freq=40 -prefs build.flash_size=4M examples/FirebaseDemo_ESP8266/FirebaseDemo_ESP8266.ino
-- cd test && make check
+- (cd test && make check)
+- (cd test/modem/ && make test)
diff --git a/src/Firebase.h b/src/Firebase.h
index c5a11263..ddec0a0d 100644
--- a/src/Firebase.h
+++ b/src/Firebase.h
@@ -91,11 +91,13 @@ class FirebaseCall {
                const char* method, const String& path,
                const String& data = "",
                FirebaseHttpClient* http = NULL);
+  virtual ~FirebaseCall() {}
+
   virtual const FirebaseError& error() const {
     return error_;
   }
 
-  virtual const String& response() {
+  virtual const String& response() const {
     return response_;
   }
 
@@ -134,6 +136,7 @@ class FirebasePush : public FirebaseCall {
   FirebasePush() {}
   FirebasePush(const String& host, const String& auth,
                const String& path, const String& value, FirebaseHttpClient* http = NULL);
+  virtual ~FirebasePush() {}
 
   virtual const String& name() const {
     return name_;
@@ -156,6 +159,7 @@ class FirebaseStream : public FirebaseCall {
   FirebaseStream() {}
   FirebaseStream(const String& host, const String& auth,
                  const String& path, FirebaseHttpClient* http = NULL);
+  virtual ~FirebaseStream() {}
 
   // Return if there is any event available to read.
   virtual bool available();