diff --git a/src/CallHandler.js b/src/CallHandler.js
index cf8460db6c..b3af0e8337 100644
--- a/src/CallHandler.js
+++ b/src/CallHandler.js
@@ -173,17 +173,27 @@ function _onAction(payload) {
             console.error("Unknown conf call type: %s", payload.type);
         }
     }
+    var ErrorDialog = sdk.getComponent("organisms.ErrorDialog");
 
     switch (payload.action) {
         case 'place_call':
             if (module.exports.getAnyActiveCall()) {
-                var ErrorDialog = sdk.getComponent("organisms.ErrorDialog");
                 Modal.createDialog(ErrorDialog, {
                     title: "Existing Call",
                     description: "You are already in a call."
                 });
                 return; // don't allow >1 call to be placed.
             }
+
+            // if the runtime env doesn't do VoIP, whine.
+            if (!MatrixClientPeg.get().supportsVoip()) {
+                Modal.createDialog(ErrorDialog, {
+                    title: "VoIP is unsupported",
+                    description: "You cannot place VoIP calls in this browser."
+                });
+                return;
+            }
+
             var room = MatrixClientPeg.get().getRoom(payload.room_id);
             if (!room) {
                 console.error("Room %s does not exist.", payload.room_id);
@@ -218,11 +228,17 @@ function _onAction(payload) {
         case 'place_conference_call':
             console.log("Place conference call in %s", payload.room_id);
             if (!Modulator.hasConferenceHandler()) {
-                var ErrorDialog = sdk.getComponent("organisms.ErrorDialog");
                 Modal.createDialog(ErrorDialog, {
                     description: "Conference calls are not supported in this client"
                 });
-            } else {
+            }
+            else if (!MatrixClientPeg.get().supportsVoip()) {
+                Modal.createDialog(ErrorDialog, {
+                    title: "VoIP is unsupported",
+                    description: "You cannot place VoIP calls in this browser."
+                });
+            }
+            else {
                 var ConferenceHandler = Modulator.getConferenceHandler();
                 ConferenceHandler.createNewMatrixCall(
                     MatrixClientPeg.get(), payload.room_id
@@ -238,6 +254,12 @@ function _onAction(payload) {
                 payload.call.hangup("busy");
                 return; // don't allow >1 call to be received, hangup newer one.
             }
+
+            // if the runtime env doesn't do VoIP, stop here.
+            if (!MatrixClientPeg.get().supportsVoip()) {
+                return;
+            }
+
             var call = payload.call;
             _setCallListeners(call);
             _setCallState(call, call.roomId, "ringing");
diff --git a/src/TextForEvent.js b/src/TextForEvent.js
index d784fa7c38..439d7b9ef5 100644
--- a/src/TextForEvent.js
+++ b/src/TextForEvent.js
@@ -1,3 +1,4 @@
+var MatrixClientPeg = require("./MatrixClientPeg");
 
 function textForMemberEvent(ev) {
     // XXX: SYJS-16 "sender is sometimes null for join messages"
@@ -78,12 +79,14 @@ function textForMessageEvent(ev) {
 
 function textForCallAnswerEvent(event) {
     var senderName = event.sender ? event.sender.name : "Someone";
-    return senderName + " answered the call.";
+    var supported = MatrixClientPeg.get().supportsVoip() ? "" : " (not supported by this browser)";
+    return senderName + " answered the call." + supported;
 };
 
 function textForCallHangupEvent(event) {
     var senderName = event.sender ? event.sender.name : "Someone";
-    return senderName + " ended the call.";
+    var supported = MatrixClientPeg.get().supportsVoip() ? "" : " (not supported by this browser)";
+    return senderName + " ended the call." + supported;
 };
 
 function textForCallInviteEvent(event) {
@@ -94,7 +97,8 @@ function textForCallInviteEvent(event) {
             event.getContent().offer.sdp.indexOf('m=video') !== -1) {
         type = "video";
     }
-    return senderName + " placed a " + type + " call.";
+    var supported = MatrixClientPeg.get().supportsVoip() ? "" : " (not supported by this browser)";
+    return senderName + " placed a " + type + " call." + supported;
 };
 
 var handlers = {