diff --git a/app/backend/computermanager.cpp b/app/backend/computermanager.cpp
index 96f11969..0f91e018 100644
--- a/app/backend/computermanager.cpp
+++ b/app/backend/computermanager.cpp
@@ -607,7 +607,7 @@ public:
     }
 
 signals:
-    void computerAddCompleted(QVariant success);
+    void computerAddCompleted(QVariant success, QVariant detectedPortBlocking);
 
     void computerStateChanged(NvComputer* computer);
 
@@ -637,7 +637,11 @@ private:
             return serverInfo;
         } catch (...) {
             if (!m_Mdns) {
-                emit computerAddCompleted(false);
+                // We failed to connect to the specified PC. Let's test to make sure this network
+                // isn't blocking Moonlight, so we can tell the user about it.
+                int portTestResult = LiTestClientConnectivity("qt.conntest.moonlight-stream.org", 443,
+                                                              ML_PORT_FLAG_TCP_47984 | ML_PORT_FLAG_TCP_47989);
+                emit computerAddCompleted(false, portTestResult != 0 && portTestResult != ML_TEST_RESULT_INCONCLUSIVE);
             }
             return QString();
         }
@@ -729,7 +733,7 @@ private:
 
                 // For non-mDNS clients, let them know it succeeded
                 if (!m_Mdns) {
-                    emit computerAddCompleted(true);
+                    emit computerAddCompleted(true, false);
                 }
 
                 // Tell our client if something changed
@@ -750,7 +754,7 @@ private:
 
                 // For non-mDNS clients, let them know it succeeded
                 if (!m_Mdns) {
-                    emit computerAddCompleted(true);
+                    emit computerAddCompleted(true, false);
                 }
 
                 // Tell our client about this new PC
diff --git a/app/backend/computermanager.h b/app/backend/computermanager.h
index 08675669..57593632 100644
--- a/app/backend/computermanager.h
+++ b/app/backend/computermanager.h
@@ -188,7 +188,7 @@ signals:
 
     void pairingCompleted(NvComputer* computer, QString error);
 
-    void computerAddCompleted(QVariant success);
+    void computerAddCompleted(QVariant success, QVariant detectedPortBlocking);
 
     void quitAppCompleted(QVariant error);
 
diff --git a/app/gui/PcView.qml b/app/gui/PcView.qml
index bb4568dc..14861277 100644
--- a/app/gui/PcView.qml
+++ b/app/gui/PcView.qml
@@ -58,11 +58,18 @@ CenteredGridView {
         }
     }
 
-    function addComplete(success)
+    function addComplete(success, detectedPortBlocking)
     {
         if (!success) {
             errorDialog.text = "Unable to connect to the specified PC."
-            errorDialog.helpText = "Click the Help button for possible solutions."
+
+            if (detectedPortBlocking) {
+                errorDialog.text += "\n\nThis PC's Internet connection is blocking Moonlight. Streaming over the Internet may not work while connected to this network."
+            }
+            else {
+                errorDialog.helpText = "Click the Help button for possible solutions."
+            }
+
             errorDialog.open()
         }
     }