diff --git a/src/CallHandler.tsx b/src/CallHandler.tsx
index eaff6ee186..f6cd54e474 100644
--- a/src/CallHandler.tsx
+++ b/src/CallHandler.tsx
@@ -54,6 +54,7 @@ import { WidgetLayoutStore, Container } from './stores/widgets/WidgetLayoutStore
 import { getIncomingCallToastKey } from './toasts/IncomingCallToast';
 import ToastStore from './stores/ToastStore';
 import IncomingCallToast from "./toasts/IncomingCallToast";
+import { SyncState } from "matrix-js-sdk/src/sync.api";
 
 export const PROTOCOL_PSTN = 'm.protocol.pstn';
 export const PROTOCOL_PSTN_PREFIXED = 'im.vector.protocol.pstn';
@@ -777,8 +778,16 @@ export default class CallHandler extends EventEmitter {
         // if the runtime env doesn't do VoIP, whine.
         if (!MatrixClientPeg.get().supportsVoip()) {
             Modal.createTrackedDialog('Call Handler', 'VoIP is unsupported', ErrorDialog, {
-                title: _t('VoIP is unsupported'),
-                description: _t('You cannot place VoIP calls in this browser.'),
+                title: _t('Calls are unsupported'),
+                description: _t('You cannot place calls in this browser.'),
+            });
+            return;
+        }
+
+        if (MatrixClientPeg.get().getSyncState() === SyncState.Error) {
+            Modal.createTrackedDialog('Call Handler', 'Sync error', ErrorDialog, {
+                title: _t('Connectivity to the server has been lost'),
+                description: _t('You cannot place calls without a connection to the server.'),
             });
             return;
         }
diff --git a/src/i18n/strings/en_EN.json b/src/i18n/strings/en_EN.json
index 1154d242ad..bc0f5da8f1 100644
--- a/src/i18n/strings/en_EN.json
+++ b/src/i18n/strings/en_EN.json
@@ -55,8 +55,10 @@
     "No other application is using the webcam": "No other application is using the webcam",
     "Already in call": "Already in call",
     "You're already in a call with this person.": "You're already in a call with this person.",
-    "VoIP is unsupported": "VoIP is unsupported",
-    "You cannot place VoIP calls in this browser.": "You cannot place VoIP calls in this browser.",
+    "Calls are unsupported": "Calls are unsupported",
+    "You cannot place calls in this browser.": "You cannot place calls in this browser.",
+    "Connectivity to the server has been lost": "Connectivity to the server has been lost",
+    "You cannot place calls without a connection to the server.": "You cannot place calls without a connection to the server.",
     "Too Many Calls": "Too Many Calls",
     "You've reached the maximum number of simultaneous calls.": "You've reached the maximum number of simultaneous calls.",
     "You cannot place a call with yourself.": "You cannot place a call with yourself.",