diff --git a/src/domain/login/CompleteOIDCLoginViewModel.js b/src/domain/login/CompleteOIDCLoginViewModel.js
index f3a9c441..ca65c7c7 100644
--- a/src/domain/login/CompleteOIDCLoginViewModel.js
+++ b/src/domain/login/CompleteOIDCLoginViewModel.js
@@ -29,6 +29,7 @@ export class CompleteOIDCLoginViewModel extends ViewModel {
         } = options;
         this._request = options.platform.request;
         this._encoding = options.platform.encoding;
+        this._crypto = options.platform.crypto;
         this._state = state;
         this._code = code;
         this._attemptLogin = attemptLogin;
@@ -63,6 +64,7 @@ export class CompleteOIDCLoginViewModel extends ViewModel {
             clientId: "hydrogen-web",
             request: this._request,
             encoding: this._encoding,
+            crypto: this._crypto,
         });
         const method = new OIDCLoginMethod({oidcApi, nonce, codeVerifier, code, homeserver, startedAt, redirectUri});
         const status = await this._attemptLogin(method);
diff --git a/src/domain/login/StartOIDCLoginViewModel.js b/src/domain/login/StartOIDCLoginViewModel.js
index 89600d58..a06b764f 100644
--- a/src/domain/login/StartOIDCLoginViewModel.js
+++ b/src/domain/login/StartOIDCLoginViewModel.js
@@ -28,6 +28,7 @@ export class StartOIDCLoginViewModel extends ViewModel {
             issuer: this._issuer,
             request: this.platform.request,
             encoding: this.platform.encoding,
+            crypto: this.platform.crypto,
         });
     }
 
diff --git a/src/matrix/Client.js b/src/matrix/Client.js
index 0eb380e5..7d0d87a0 100644
--- a/src/matrix/Client.js
+++ b/src/matrix/Client.js
@@ -135,6 +135,7 @@ export class Client {
                         clientId: "hydrogen-web",
                         request: this._platform.request,
                         encoding: this._platform.encoding,
+                        crypto: this._platform.crypto,
                     });
                     await oidcApi.validate();
 
@@ -265,6 +266,7 @@ export class Client {
                 clientId: "hydrogen-web",
                 request: this._platform.request,
                 encoding: this._platform.encoding,
+                crypto: this._platform.crypto,
             });
 
             // TODO: stop/pause the refresher?
diff --git a/src/matrix/net/OidcApi.ts b/src/matrix/net/OidcApi.ts
index 3dfe4cdd..f7c08dca 100644
--- a/src/matrix/net/OidcApi.ts
+++ b/src/matrix/net/OidcApi.ts
@@ -54,14 +54,16 @@ export class OidcApi {
     _issuer: string;
     _clientId: string;
     _requestFn: any;
-    _base64: any;
+    _encoding: any;
+    _crypto: any;
     _metadataPromise: Promise<any>;
 
-    constructor({ issuer, clientId, request, encoding }) {
+    constructor({ issuer, clientId, request, encoding, crypto }) {
         this._issuer = issuer;
         this._clientId = clientId;
         this._requestFn = request;
-        this._base64 = encoding.base64;
+        this._encoding = encoding;
+        this._crypto = crypto;
     }
 
     get metadataUrl() {
@@ -110,10 +112,9 @@ export class OidcApi {
     async _generateCodeChallenge(
         codeVerifier: string
     ): Promise<string> {
-        const encoder = new TextEncoder();
-        const data = encoder.encode(codeVerifier);
-        const digest = await window.crypto.subtle.digest("SHA-256", data);
-        const base64Digest = this._base64.encode(digest);
+        const data = this._encoding.utf8.encode(codeVerifier);
+        const digest = await this._crypto.digest("SHA-256", data);
+        const base64Digest = this._encoding.base64.encode(digest);
         return base64Digest.replace(/\+/g, "-").replace(/\//g, "_").replace(/=/g, "");
     }