diff --git a/src/Preferences.js b/src/Preferences.js
index d6d36f6..d365230 100644
--- a/src/Preferences.js
+++ b/src/Preferences.js
@@ -25,6 +25,7 @@ export class Preferences extends EventEmitter {
         // used to differentiate web from native if a client supports both
         this.platform = null;
         this.homeservers = null;
+        this.customWebInstances = {};
 
         const prefsStr = localStorage.getItem("preferred_client");
         if (prefsStr) {
@@ -36,6 +37,10 @@ export class Preferences extends EventEmitter {
         if (serversStr) {
             this.homeservers = JSON.parse(serversStr);
         }
+        const customWebInstancesStr = localStorage.getItem("custom_web_instances");
+        if (customWebInstancesStr) {
+            this.customWebInstances = JSON.parse(customWebInstancesStr);
+        }
     }
 
     setClient(id, platform) {
@@ -54,15 +59,27 @@ export class Preferences extends EventEmitter {
         }
     }
 
+    setCustomWebInstance(client_id, instance_url) {
+        this.customWebInstances[client_id] = instance_url;
+        this._localStorage.setItem("custom_web_instances", JSON.stringify(this.customWebInstances));
+        this.emit("canClear");
+    }
+
+    getCustomWebInstance(client_id) {
+        return this.customWebInstances[client_id];
+    }
+
     clear() {
         this._localStorage.removeItem("preferred_client");
         this._localStorage.removeItem("consented_servers");
+        this._localStorage.removeItem("custom_web_instances");
         this.clientId = null;
         this.platform = null;
         this.homeservers = null;
+        this.customWebInstances = {};
     }
 
     get canClear() {
-        return !!this.clientId || !!this.platform || !!this.homeservers;
+        return !!this.clientId || !!this.platform || !!this.homeservers || !!this.customWebInstances;
     }
 }
diff --git a/src/open/ClientView.js b/src/open/ClientView.js
index 76c73e9..c73b682 100644
--- a/src/open/ClientView.js
+++ b/src/open/ClientView.js
@@ -39,6 +39,14 @@ function renderInstructions(parts) {
 export class ClientView extends TemplateView {
 
     render(t, vm) {
+        return t.mapView(vm => vm.customWebInstanceFormOpen, open => {
+            switch (open) {
+                case true: return new SetCustomWebInstanceView(vm);
+                case false: return new TemplateView(vm, t => this.renderContent(t, vm));
+            }
+        });
+    }
+    renderContent(t, vm) {
         return t.div({className: {"ClientView": true, "isPreferred": vm => vm.hasPreferredWebInstance}}, [
             ... vm.hasPreferredWebInstance ? [t.div({className: "hostedBanner"}, vm.hostedByBannerLabel)] : [],
             t.div({className: "header"}, [
@@ -112,10 +120,49 @@ class InstallClientView extends TemplateView {
     }
 }
 
+export class SetCustomWebInstanceView extends TemplateView {
+    render(t, vm) {
+        return t.div({className: "SetCustomWebInstanceView"}, [
+            t.p([
+                "Use a custom web instance for the ", t.strong(vm.name), " client:",
+            ]),
+            t.form({action: "#", id: "setCustomWebInstanceForm", onSubmit: evt => this._onSubmit(evt)}, [
+                t.input({
+                    type: "text",
+                    className: "fullwidth large",
+                    placeholder: "chat.example.org",
+                    name: "instanceHostname",
+                    value: vm.preferredWebInstance || "",
+                }),
+                t.input({type: "submit", value: "Save", className: "primary fullwidth"}),
+                t.input({type: "button", value: "Use Default Instance", className: "secondary fullwidth", onClick: evt => this._onReset(evt)}),
+            ])
+        ]);
+    }
+
+    _onSubmit(evt) {
+        evt.preventDefault();
+        const form = evt.target;
+        const {instanceHostname} = form.elements;
+        this.value.setCustomWebInstance(instanceHostname.value);
+        this.value.closeCustomWebInstanceForm();
+    }
+
+    _onReset(evt) {
+        this.value.setCustomWebInstance(undefined);
+        this.value.closeCustomWebInstanceForm();
+    }
+}
+
 function showBack(t, vm) {
     return t.p({className: {caption: true, "back": true, hidden: vm => !vm.showBack}}, [
         `Continue with ${vm.name} · `,
         t.button({className: "text", onClick: () => vm.back()}, "Change"),
+        t.span({hidden: vm => !vm.supportsCustomWebInstances}, [
+            ' · ',
+            t.button({className: "text", onClick: () => vm.configureCustomWebInstance()}, "Use Custom Web Instance"),
+        ])
+
     ]);
 }
 
diff --git a/src/open/ClientViewModel.js b/src/open/ClientViewModel.js
index 2cd7244..210e30b 100644
--- a/src/open/ClientViewModel.js
+++ b/src/open/ClientViewModel.js
@@ -35,6 +35,7 @@ export class ClientViewModel extends ViewModel {
         this._pickClient = pickClient;
         // to provide "choose other client" button after calling pick()
         this._clientListViewModel = null;
+        this.customWebInstanceFormOpen = false;
         this._update();
     }
 
@@ -59,11 +60,11 @@ export class ClientViewModel extends ViewModel {
             if (this._proposedPlatform === this._nativePlatform) {
                 deepLinkLabel = "Open in app";
             } else {
-                deepLinkLabel = `Open on ${this._client.getPreferredWebInstance(this._link)}`;
+                deepLinkLabel = `Open on ${this.preferredWebInstance}`;
             }
         }
         const actions = [];
-        const proposedDeepLink = this._client.getDeepLink(this._proposedPlatform, this._link);
+        const proposedDeepLink = this._client.getDeepLink(this._proposedPlatform, this._link, this.preferredWebInstance);
         if (proposedDeepLink) {
             actions.push({
                 label: deepLinkLabel,
@@ -83,8 +84,8 @@ export class ClientViewModel extends ViewModel {
         // show only if there is a preferred instance, and if we don't already link to it in the first button
         if (hasPreferredWebInstance && this._webPlatform && this._proposedPlatform !== this._webPlatform) {
             actions.push({
-                label: `Open on ${this._client.getPreferredWebInstance(this._link)}`,
-                url: this._client.getDeepLink(this._webPlatform, this._link),
+                label: `Open on ${this.preferredWebInstance}`,
+                url: this._client.getDeepLink(this._webPlatform, this._link, this.preferredWebInstance),
                 kind: "open-in-web",
                 activated: () => {} // don't persist this choice as we don't persist the preferred web instance, it's in the url
             });
@@ -108,10 +109,10 @@ export class ClientViewModel extends ViewModel {
             actions.push(...nativeActions);
         }
         if (this._webPlatform) {
-            const webDeepLink = this._client.getDeepLink(this._webPlatform, this._link);
+            const webDeepLink = this._client.getDeepLink(this._webPlatform, this._link, this.preferredWebInstance);
             if (webDeepLink) {
                 const webLabel = this.hasPreferredWebInstance ?
-                    `Open on ${this._client.getPreferredWebInstance(this._link)}` :
+                    `Open on ${this.preferredWebInstance}` :
                     `Continue in your browser`;
                 actions.push({
                     label: webLabel,
@@ -128,18 +129,26 @@ export class ClientViewModel extends ViewModel {
         return actions;
     }
 
-    get hasPreferredWebInstance() {
+    get preferredWebInstance() {
         // also check there is a web platform that matches the platforms the user is on (mobile or desktop web)
-        return this._webPlatform && typeof this._client.getPreferredWebInstance(this._link) === "string";
+        if (!this._webPlatform) return undefined;
+        return (
+            this.preferences.getCustomWebInstance(this._client.id)
+            || this._client.getPreferredWebInstance(this._link)
+        );
+    }
+
+    get hasPreferredWebInstance() {
+        return typeof this.preferredWebInstance === "string";
     }
 
     get hostedByBannerLabel() {
-        const preferredWebInstance = this._client.getPreferredWebInstance(this._link);
-        if (this._webPlatform && preferredWebInstance) {
+        if (this.hasPreferredWebInstance) {
+            const preferredWebInstance = this.preferredWebInstance;
             let label = preferredWebInstance;
-            const subDomainIdx = preferredWebInstance.lastIndexOf(".", preferredWebInstance.lastIndexOf("."));
+            const subDomainIdx = preferredWebInstance.lastIndexOf(".", preferredWebInstance.lastIndexOf(".") - 1);
             if (subDomainIdx !== -1) {
-                label = preferredWebInstance.slice(preferredWebInstance.length - subDomainIdx + 1);
+                label = preferredWebInstance.slice(subDomainIdx + 1);
             }
             return `Hosted by ${label}`;
         }
@@ -188,7 +197,7 @@ export class ClientViewModel extends ViewModel {
 
     get showDeepLinkInInstall() {
         // we can assume this._nativePlatform as this._clientCanIntercept already checks it
-        return this._clientCanIntercept && !!this._client.getDeepLink(this._nativePlatform, this._link);
+        return this._clientCanIntercept && !!this._client.getDeepLink(this._nativePlatform, this._link, this.preferredWebInstance);
     }
 
     get availableOnPlatformNames() {
@@ -223,6 +232,10 @@ export class ClientViewModel extends ViewModel {
         return !!this._clientListViewModel;
     }
 
+    get supportsCustomWebInstances() {
+        return !!this._client.supportsCustomInstances;
+    }
+
     back() {
         if (this._clientListViewModel) {
             const vm = this._clientListViewModel;
@@ -231,9 +244,29 @@ export class ClientViewModel extends ViewModel {
             // in the list with all clients, and also if we refresh, we get the list with
             // all clients rather than having our "change client" click reverted.
             this.preferences.setClient(undefined, undefined);
+            this.preferences.setCustomWebInstance(this._client.id, undefined);
             this._update();
             this.emitChange();
             vm.showAll();
         }
     }
+
+    configureCustomWebInstance() {
+        this.customWebInstanceFormOpen = true;
+        this.emitChange();
+    }
+
+    closeCustomWebInstanceForm() {
+        this.customWebInstanceFormOpen = false;
+        this.emitChange();
+    }
+
+    setCustomWebInstance(hostname) {
+        if (hostname) {
+            hostname = hostname.trim().replace(/^https:\/\//, '').replace(/\/.*$/, '');
+        }
+        this.preferences.setClient(this._client.id, hostname ? this._webPlatform : (this._nativePlatform || this._webPlatform));
+        this.preferences.setCustomWebInstance(this._client.id, hostname || undefined);
+        this._update();
+    }
 }
diff --git a/src/open/clients/Element.js b/src/open/clients/Element.js
index 06ca2fe..e28b0ac 100644
--- a/src/open/clients/Element.js
+++ b/src/open/clients/Element.js
@@ -55,8 +55,9 @@ export class Element {
     get homepage() { return "https://element.io"; }
     get author() { return "Element"; }
     getMaturity(platform) { return Maturity.Stable; }
+    get supportsCustomInstances() { return true; }
 
-    getDeepLink(platform, link) {
+    getDeepLink(platform, link, preferredWebInstance) {
         let fragmentPath;
         switch (link.kind) {
             case LinkKind.User:
@@ -82,8 +83,8 @@ export class Element {
             let instanceHost = trustedWebInstances[0];
             // we use app.element.io which iOS will intercept, but it likely won't intercept any other trusted instances
             // so only use a preferred web instance for true web links.
-            if (isWebPlatform && trustedWebInstances.includes(link.webInstances[this.id])) {
-                instanceHost = link.webInstances[this.id];
+            if (isWebPlatform && preferredWebInstance) {
+                instanceHost = preferredWebInstance;
             }
             return `https://${instanceHost}/#/${fragmentPath}`;
         } else if (platform === Platform.Linux || platform === Platform.Windows || platform === Platform.macOS) {