diff --git a/Signal/src/AppDelegate.m b/Signal/src/AppDelegate.m
index ca903eb09..52851aa24 100644
--- a/Signal/src/AppDelegate.m
+++ b/Signal/src/AppDelegate.m
@@ -334,8 +334,55 @@ static NSString *const kURLHostVerifyPrefix             = @"verify";
 - (BOOL)application:(UIApplication *)application continueUserActivity:(nonnull NSUserActivity *)userActivity restorationHandler:(nonnull void (^)(NSArray * _Nullable))restorationHandler
 {
     if ([userActivity.activityType isEqualToString:@"INStartVideoCallIntent"]) {
+        if (!SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(10, 0)) {
+            DDLogError(@"%@ unexpectedly received INStartVideoCallIntent pre iOS10", self.tag);
+            return NO;
+        }
+
         DDLogInfo(@"%@ got start video call intent", self.tag);
-        [[Environment getCurrent].callService handleCallKitStartVideo];
+
+        INInteraction *interaction = [userActivity interaction];
+        INIntent *intent = interaction.intent;
+
+        if (![intent isKindOfClass:[INStartVideoCallIntent class]]) {
+            DDLogError(@"%@ unexpected class for start call video: %@", self.tag, intent);
+            return NO;
+        }
+        INStartVideoCallIntent *startCallIntent = (INStartVideoCallIntent *)intent;
+        NSString *_Nullable handle = startCallIntent.contacts.firstObject.personHandle.value;
+        if (!handle) {
+            DDLogWarn(@"%@ unable to find handle in startCallIntent: %@", self.tag, startCallIntent);
+            return NO;
+        }
+
+        if ([Environment getCurrent].phoneManager.hasOngoingCall) {
+            DDLogWarn(@"%@ ignoring INStartVideoCallIntent due to ongoing RedPhone call.", self.tag);
+            return NO;
+        }
+
+        // This intent can be received from more than one user interaction.
+        //
+        // * It can be received if the user taps the "video" button in the CallKit UI for an
+        //   an ongoing call.  If so, the correct response is to try to activate the local
+        //   video for that call.
+        // * It can be received if the user taps the "video" button for a contact in the
+        //   contacts app.  If so, the correct response is to try to initiate a new call
+        //   to that user - unless there already is another call in progress.
+        if ([Environment getCurrent].callService.call != nil) {
+            if ([handle isEqualToString:[Environment getCurrent].callService.call.remotePhoneNumber]) {
+                DDLogWarn(@"%@ trying to upgrade ongoing call to video.", self.tag);
+                [[Environment getCurrent].callService handleCallKitStartVideo];
+                return YES;
+            } else {
+                DDLogWarn(
+                    @"%@ ignoring INStartVideoCallIntent due to ongoing WebRTC call with another party.", self.tag);
+                return NO;
+            }
+        }
+
+        OutboundCallInitiator *outboundCallInitiator = [Environment getCurrent].outboundCallInitiator;
+        OWSAssert(outboundCallInitiator);
+        return [outboundCallInitiator initiateCallWithHandle:handle];
     } else if ([userActivity.activityType isEqualToString:@"INStartAudioCallIntent"]) {
 
         if (!SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(10, 0)) {
@@ -359,6 +406,15 @@ static NSString *const kURLHostVerifyPrefix             = @"verify";
             return NO;
         }
 
+        if ([Environment getCurrent].phoneManager.hasOngoingCall) {
+            DDLogWarn(@"%@ ignoring INStartAudioCallIntent due to ongoing RedPhone call.", self.tag);
+            return NO;
+        }
+        if ([Environment getCurrent].callService.call != nil) {
+            DDLogWarn(@"%@ ignoring INStartAudioCallIntent due to ongoing WebRTC call.", self.tag);
+            return NO;
+        }
+
         OutboundCallInitiator *outboundCallInitiator = [Environment getCurrent].outboundCallInitiator;
         OWSAssert(outboundCallInitiator);
         return [outboundCallInitiator initiateCallWithHandle:handle];
diff --git a/Signal/src/call/OutboundCallInitiator.swift b/Signal/src/call/OutboundCallInitiator.swift
index 547357ab5..f62854bb0 100644
--- a/Signal/src/call/OutboundCallInitiator.swift
+++ b/Signal/src/call/OutboundCallInitiator.swift
@@ -52,6 +52,16 @@ import Foundation
         // SignalRecipient *recipient = [SignalRecipient recipientWithTextSecureIdentifier:self.thread.contactIdentifier];
         self.contactsUpdater.lookupIdentifier(recipientId,
                                               success: { recipient in
+
+                                                guard !Environment.getCurrent().phoneManager.hasOngoingCall() else {
+                                                    Logger.error("\(self.TAG) OutboundCallInitiator aborting due to ongoing RedPhone call.")
+                                                    return
+                                                }
+                                                guard Environment.getCurrent().callService.call != nil else {
+                                                    Logger.error("\(self.TAG) OutboundCallInitiator aborting due to ongoing WebRTC call.")
+                                                    return
+                                                }
+
                                                 let remoteWantsWebRTC = recipient.supportsWebRTC
                                                 Logger.debug("\(self.TAG) localWantsWebRTC: \(localWantsWebRTC), remoteWantsWebRTC: \(remoteWantsWebRTC)")
 
diff --git a/Signal/src/phone/PhoneManager.h b/Signal/src/phone/PhoneManager.h
index 168f6580f..fb793bc3b 100644
--- a/Signal/src/phone/PhoneManager.h
+++ b/Signal/src/phone/PhoneManager.h
@@ -1,3 +1,7 @@
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
+
 #import <Foundation/Foundation.h>
 #import "CallAudioManager.h"
 #import "CallConnectUtil.h"
@@ -36,6 +40,9 @@
 - (BOOL)toggleMute;
 - (void)backgroundTimeExpired;
 
+// Returns YES IFF there is an ongoing RedPhone call.
+- (BOOL)hasOngoingCall;
+
 - (ObservableValue *)currentCallObservable;
 
 + (PhoneManager *)phoneManagerWithErrorHandler:(ErrorHandlerBlock)errorHandler;
diff --git a/Signal/src/phone/PhoneManager.m b/Signal/src/phone/PhoneManager.m
index 120a51bd4..d8caa2a96 100644
--- a/Signal/src/phone/PhoneManager.m
+++ b/Signal/src/phone/PhoneManager.m
@@ -1,3 +1,7 @@
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
+
 #import "AppAudioManager.h"
 #import "CallAudioManager.h"
 #import "PhoneManager.h"
@@ -132,6 +136,12 @@
     }
                                                                               incoming:YES];
 }
+
+- (BOOL)hasOngoingCall
+{
+    return self.curCallController != nil;
+}
+
 - (CallController *)curCallController {
     return currentCallControllerObservable.currentValue;
 }