diff --git a/dom/mobileconnection/Assertions.cpp b/dom/mobileconnection/Assertions.cpp
index b544011334a..be5e53b0d1e 100644
--- a/dom/mobileconnection/Assertions.cpp
+++ b/dom/mobileconnection/Assertions.cpp
@@ -28,5 +28,24 @@ ASSERT_MOBILE_RADIO_STATE_EQUALITY(Disabled, MOBILE_RADIO_STATE_DISABLED);
 
 #undef ASSERT_MOBILE_RADIO_STATE_EQUALITY
 
+#define ASSERT_PREFERRED_NETWORK_TYPE_EQUALITY(webidlState, xpidlState) \
+  static_assert(static_cast<int32_t>(MobilePreferredNetworkType::webidlState) == nsIMobileConnection::xpidlState, \
+                "MobilePreferredNetworkType::" #webidlState " should equal to nsIMobileConnection::" #xpidlState)
+
+ASSERT_PREFERRED_NETWORK_TYPE_EQUALITY(Wcdma_gsm, PREFERRED_NETWORK_TYPE_WCDMA_GSM);
+ASSERT_PREFERRED_NETWORK_TYPE_EQUALITY(Gsm, PREFERRED_NETWORK_TYPE_GSM_ONLY);
+ASSERT_PREFERRED_NETWORK_TYPE_EQUALITY(Wcdma, PREFERRED_NETWORK_TYPE_WCDMA_ONLY);
+ASSERT_PREFERRED_NETWORK_TYPE_EQUALITY(Wcdma_gsm_auto, PREFERRED_NETWORK_TYPE_WCDMA_GSM_AUTO);
+ASSERT_PREFERRED_NETWORK_TYPE_EQUALITY(Cdma_evdo, PREFERRED_NETWORK_TYPE_CDMA_EVDO);
+ASSERT_PREFERRED_NETWORK_TYPE_EQUALITY(Cdma, PREFERRED_NETWORK_TYPE_CDMA_ONLY);
+ASSERT_PREFERRED_NETWORK_TYPE_EQUALITY(Evdo, PREFERRED_NETWORK_TYPE_EVDO_ONLY);
+ASSERT_PREFERRED_NETWORK_TYPE_EQUALITY(Wcdma_gsm_cdma_evdo, PREFERRED_NETWORK_TYPE_WCDMA_GSM_CDMA_EVDO);
+ASSERT_PREFERRED_NETWORK_TYPE_EQUALITY(Lte_cdma_evdo, PREFERRED_NETWORK_TYPE_LTE_CDMA_EVDO);
+ASSERT_PREFERRED_NETWORK_TYPE_EQUALITY(Lte_wcdma_gsm, PREFERRED_NETWORK_TYPE_LTE_WCDMA_GSM);
+ASSERT_PREFERRED_NETWORK_TYPE_EQUALITY(Lte_wcdma_gsm_cdma_evdo, PREFERRED_NETWORK_TYPE_LTE_WCDMA_GSM_CDMA_EVDO);
+ASSERT_PREFERRED_NETWORK_TYPE_EQUALITY(Lte, PREFERRED_NETWORK_TYPE_LTE_ONLY);
+
+#undef ASSERT_PREFERRED_NETWORK_TYPE_EQUALITY
+
 } // namespace dom
 } // namespace mozilla
diff --git a/dom/mobileconnection/MobileConnection.cpp b/dom/mobileconnection/MobileConnection.cpp
index 33c02ff79a1..1dc97443a16 100644
--- a/dom/mobileconnection/MobileConnection.cpp
+++ b/dom/mobileconnection/MobileConnection.cpp
@@ -477,8 +477,7 @@ MobileConnection::SetPreferredNetworkType(MobilePreferredNetworkType& aType,
     return nullptr;
   }
 
-  nsAutoString type;
-  CONVERT_ENUM_TO_STRING(MobilePreferredNetworkType, aType, type);
+  int32_t type = static_cast<int32_t>(aType);
 
   nsRefPtr<DOMRequest> request = new DOMRequest(GetOwner());
   nsRefPtr<MobileConnectionCallback> requestCallback =
diff --git a/dom/mobileconnection/MobileConnectionCallback.cpp b/dom/mobileconnection/MobileConnectionCallback.cpp
index 121b5b1e6ab..bc81a327a5a 100644
--- a/dom/mobileconnection/MobileConnectionCallback.cpp
+++ b/dom/mobileconnection/MobileConnectionCallback.cpp
@@ -15,6 +15,13 @@ namespace mozilla {
 namespace dom {
 namespace mobileconnection {
 
+#define CONVERT_ENUM_TO_STRING(_enumType, _enum, _string)               \
+{                                                                       \
+  uint32_t index = uint32_t(_enum);                                     \
+  _string.AssignASCII(_enumType##Values::strings[index].value,          \
+                      _enumType##Values::strings[index].length);        \
+}
+
 NS_IMPL_ISUPPORTS(MobileConnectionCallback, nsIMobileConnectionCallback)
 
 MobileConnectionCallback::MobileConnectionCallback(nsPIDOMWindow* aWindow,
@@ -349,6 +356,18 @@ MobileConnectionCallback::NotifyGetClirStatusSuccess(uint16_t aN, uint16_t aM)
   return NotifySuccess(jsResult);
 };
 
+NS_IMETHODIMP
+MobileConnectionCallback::NotifyGetPreferredNetworkTypeSuccess(int32_t aType)
+{
+  MOZ_ASSERT(aType < static_cast<int32_t>(MobilePreferredNetworkType::EndGuard_));
+  MobilePreferredNetworkType type = static_cast<MobilePreferredNetworkType>(aType);
+
+  nsAutoString typeString;
+  CONVERT_ENUM_TO_STRING(MobilePreferredNetworkType, type, typeString);
+
+  return NotifySuccessWithString(typeString);
+};
+
 NS_IMETHODIMP
 MobileConnectionCallback::NotifyError(const nsAString& aName,
                                       const nsAString& aMessage,
diff --git a/dom/mobileconnection/ipc/MobileConnectionChild.cpp b/dom/mobileconnection/ipc/MobileConnectionChild.cpp
index 61d72455502..41b907153d2 100644
--- a/dom/mobileconnection/ipc/MobileConnectionChild.cpp
+++ b/dom/mobileconnection/ipc/MobileConnectionChild.cpp
@@ -178,11 +178,10 @@ MobileConnectionChild::SelectNetworkAutomatically(nsIMobileConnectionCallback* a
 
 
 NS_IMETHODIMP
-MobileConnectionChild::SetPreferredNetworkType(const nsAString& aType,
+MobileConnectionChild::SetPreferredNetworkType(int32_t aType,
                                                nsIMobileConnectionCallback* aCallback)
 {
-  return SendRequest(SetPreferredNetworkTypeRequest(nsAutoString(aType)),
-                     aCallback)
+  return SendRequest(SetPreferredNetworkTypeRequest(aType), aCallback)
     ? NS_OK : NS_ERROR_FAILURE;
 }
 
@@ -661,6 +660,12 @@ MobileConnectionRequestChild::DoReply(const MobileConnectionReplySuccessClirStat
                                                                    aReply.m()));
 }
 
+bool
+MobileConnectionRequestChild::DoReply(const MobileConnectionReplySuccessPreferredNetworkType& aReply)
+{
+  return NS_SUCCEEDED(mRequestCallback->NotifyGetPreferredNetworkTypeSuccess(aReply.type()));
+}
+
 bool
 MobileConnectionRequestChild::DoReply(const MobileConnectionReplyError& aReply)
 {
@@ -715,6 +720,8 @@ MobileConnectionRequestChild::Recv__delete__(const MobileConnectionReply& aReply
       return DoReply(aReply.get_MobileConnectionReplySuccessCallBarring());
     case MobileConnectionReply::TMobileConnectionReplySuccessClirStatus:
       return DoReply(aReply.get_MobileConnectionReplySuccessClirStatus());
+    case MobileConnectionReply::TMobileConnectionReplySuccessPreferredNetworkType:
+      return DoReply(aReply.get_MobileConnectionReplySuccessPreferredNetworkType());
     case MobileConnectionReply::TMobileConnectionReplyError:
       return DoReply(aReply.get_MobileConnectionReplyError());
     case MobileConnectionReply::TMobileConnectionReplyErrorMmi:
diff --git a/dom/mobileconnection/ipc/MobileConnectionChild.h b/dom/mobileconnection/ipc/MobileConnectionChild.h
index d549ee8ebcc..f2532ebe5ef 100644
--- a/dom/mobileconnection/ipc/MobileConnectionChild.h
+++ b/dom/mobileconnection/ipc/MobileConnectionChild.h
@@ -163,6 +163,9 @@ public:
   bool
   DoReply(const MobileConnectionReplySuccessClirStatus& aReply);
 
+  bool
+  DoReply(const MobileConnectionReplySuccessPreferredNetworkType& aReply);
+
   bool
   DoReply(const MobileConnectionReplyError& aReply);
 
diff --git a/dom/mobileconnection/ipc/MobileConnectionParent.cpp b/dom/mobileconnection/ipc/MobileConnectionParent.cpp
index c8e4b91c5ad..3413bc423b0 100644
--- a/dom/mobileconnection/ipc/MobileConnectionParent.cpp
+++ b/dom/mobileconnection/ipc/MobileConnectionParent.cpp
@@ -642,6 +642,12 @@ MobileConnectionRequestParent::NotifyGetClirStatusSuccess(uint16_t aN,
   return SendReply(MobileConnectionReplySuccessClirStatus(aN, aM));
 }
 
+NS_IMETHODIMP
+MobileConnectionRequestParent::NotifyGetPreferredNetworkTypeSuccess(int32_t aType)
+{
+  return SendReply(MobileConnectionReplySuccessPreferredNetworkType(aType));
+}
+
 NS_IMETHODIMP
 MobileConnectionRequestParent::NotifyError(const nsAString& aName,
                                            const nsAString& aMessage,
diff --git a/dom/mobileconnection/ipc/PMobileConnection.ipdl b/dom/mobileconnection/ipc/PMobileConnection.ipdl
index 70eaba2c412..d118c7ffd1c 100644
--- a/dom/mobileconnection/ipc/PMobileConnection.ipdl
+++ b/dom/mobileconnection/ipc/PMobileConnection.ipdl
@@ -72,7 +72,7 @@ struct SelectNetworkAutoRequest
 
 struct SetPreferredNetworkTypeRequest
 {
-  nsString type;
+  int32_t type;
 };
 
 struct GetPreferredNetworkTypeRequest
diff --git a/dom/mobileconnection/ipc/PMobileConnectionRequest.ipdl b/dom/mobileconnection/ipc/PMobileConnectionRequest.ipdl
index e224bc368e1..bf2071dc0b6 100644
--- a/dom/mobileconnection/ipc/PMobileConnectionRequest.ipdl
+++ b/dom/mobileconnection/ipc/PMobileConnectionRequest.ipdl
@@ -70,6 +70,11 @@ struct MobileConnectionReplySuccessClirStatus
   uint16_t m;
 };
 
+struct MobileConnectionReplySuccessPreferredNetworkType
+{
+  int32_t type;
+};
+
 // Error
 struct MobileConnectionReplyError
 {
@@ -95,6 +100,7 @@ union MobileConnectionReply
   MobileConnectionReplySuccessCallForwarding;
   MobileConnectionReplySuccessCallBarring;
   MobileConnectionReplySuccessClirStatus;
+  MobileConnectionReplySuccessPreferredNetworkType;
   // Error
   MobileConnectionReplyError;
   MobileConnectionReplyErrorMmi;