diff --git a/app/src/main/kotlin/app/dapk/st/graph/AppModule.kt b/app/src/main/kotlin/app/dapk/st/graph/AppModule.kt
index dd4f8a4..7f7bc4d 100644
--- a/app/src/main/kotlin/app/dapk/st/graph/AppModule.kt
+++ b/app/src/main/kotlin/app/dapk/st/graph/AppModule.kt
@@ -7,10 +7,7 @@ import android.content.Intent
 import app.dapk.db.DapkDb
 import app.dapk.st.BuildConfig
 import app.dapk.st.SharedPreferencesDelegate
-import app.dapk.st.core.BuildMeta
-import app.dapk.st.core.CoreAndroidModule
-import app.dapk.st.core.CoroutineDispatchers
-import app.dapk.st.core.SingletonFlows
+import app.dapk.st.core.*
 import app.dapk.st.core.extensions.ErrorTracker
 import app.dapk.st.core.extensions.unsafeLazy
 import app.dapk.st.directory.DirectoryModule
@@ -208,7 +205,7 @@ internal class MatrixModules(
                 installAuthService(credentialsStore)
                 installEncryptionService(store.knownDevicesStore())
 
-                val olmAccountStore = OlmPersistenceWrapper(store.olmStore())
+                val olmAccountStore = OlmPersistenceWrapper(store.olmStore(), AndroidBase64())
                 val singletonFlows = SingletonFlows(coroutineDispatchers)
                 val olm = OlmWrapper(
                     olmStore = olmAccountStore,
@@ -417,3 +414,13 @@ class TaskRunnerAdapter(private val matrixTaskRunner: suspend (MatrixTask) -> Ma
         }
     }
 }
+
+class AndroidBase64 : Base64 {
+    override fun encode(input: ByteArray): String {
+        return android.util.Base64.encodeToString(input, android.util.Base64.DEFAULT)
+    }
+
+    override fun decode(input: String): ByteArray {
+        return android.util.Base64.decode(input, android.util.Base64.DEFAULT)
+    }
+}
\ No newline at end of file
diff --git a/core/src/main/kotlin/app/dapk/st/core/Base64.kt b/core/src/main/kotlin/app/dapk/st/core/Base64.kt
new file mode 100644
index 0000000..3ad71f3
--- /dev/null
+++ b/core/src/main/kotlin/app/dapk/st/core/Base64.kt
@@ -0,0 +1,6 @@
+package app.dapk.st.core
+
+interface Base64 {
+    fun encode(input: ByteArray): String
+    fun decode(input: String): ByteArray
+}
\ No newline at end of file
diff --git a/domains/olm/src/main/kotlin/app/dapk/st/olm/OlmPersistenceWrapper.kt b/domains/olm/src/main/kotlin/app/dapk/st/olm/OlmPersistenceWrapper.kt
index 36869c1..c924186 100644
--- a/domains/olm/src/main/kotlin/app/dapk/st/olm/OlmPersistenceWrapper.kt
+++ b/domains/olm/src/main/kotlin/app/dapk/st/olm/OlmPersistenceWrapper.kt
@@ -1,5 +1,6 @@
 package app.dapk.st.olm
 
+import app.dapk.st.core.Base64
 import app.dapk.st.domain.OlmPersistence
 import app.dapk.st.domain.SerializedObject
 import app.dapk.st.matrix.common.Curve25519
@@ -10,10 +11,10 @@ import org.matrix.olm.OlmInboundGroupSession
 import org.matrix.olm.OlmOutboundGroupSession
 import org.matrix.olm.OlmSession
 import java.io.*
-import java.util.*
 
 class OlmPersistenceWrapper(
     private val olmPersistence: OlmPersistence,
+    private val base64: Base64,
 ) : OlmStore {
 
     override suspend fun read(): OlmAccount? {
@@ -49,21 +50,21 @@ class OlmPersistenceWrapper(
     override suspend fun readInbound(sessionId: SessionId): OlmInboundGroupSession? {
         return olmPersistence.readInbound(sessionId)?.value?.deserialize()
     }
-}
 
-private fun <T : Serializable> T.serialize(): String {
-    val baos = ByteArrayOutputStream()
-    ObjectOutputStream(baos).use {
-        it.writeObject(this)
+    private fun <T : Serializable> T.serialize(): String {
+        val baos = ByteArrayOutputStream()
+        ObjectOutputStream(baos).use {
+            it.writeObject(this)
+        }
+        return base64.encode(baos.toByteArray())
     }
-    return Base64.getEncoder().encode(baos.toByteArray()).toString(Charsets.UTF_8)
-}
 
-@Suppress("UNCHECKED_CAST")
-private fun <T : Serializable> String.deserialize(): T {
-    val decoded = Base64.getDecoder().decode(this)
-    val baos = ByteArrayInputStream(decoded)
-    return ObjectInputStream(baos).use {
-        it.readObject() as T
+    @Suppress("UNCHECKED_CAST")
+    private fun <T : Serializable> String.deserialize(): T {
+        val decoded = base64.decode(this)
+        val baos = ByteArrayInputStream(decoded)
+        return ObjectInputStream(baos).use {
+            it.readObject() as T
+        }
     }
 }
diff --git a/test-harness/src/test/kotlin/test/TestMatrix.kt b/test-harness/src/test/kotlin/test/TestMatrix.kt
index c5de509..d38e91f 100644
--- a/test-harness/src/test/kotlin/test/TestMatrix.kt
+++ b/test-harness/src/test/kotlin/test/TestMatrix.kt
@@ -1,6 +1,7 @@
 package test
 
 import TestUser
+import app.dapk.st.core.Base64
 import app.dapk.st.core.CoroutineDispatchers
 import app.dapk.st.core.SingletonFlows
 import app.dapk.st.domain.StoreModule
@@ -81,7 +82,7 @@ class TestMatrix(
             installAuthService(storeModule.credentialsStore(), AuthConfig(forceHttp = false))
             installEncryptionService(storeModule.knownDevicesStore())
 
-            val olmAccountStore = OlmPersistenceWrapper(storeModule.olmStore())
+            val olmAccountStore = OlmPersistenceWrapper(storeModule.olmStore(), JavaBase64())
             val olm = OlmWrapper(
                 olmStore = olmAccountStore,
                 singletonFlows = SingletonFlows(coroutineDispatchers),
@@ -271,3 +272,13 @@ class TestMatrix(
     suspend fun deviceId() = storeModule.credentialsStore().credentials()!!.deviceId
     suspend fun userId() = storeModule.credentialsStore().credentials()!!.userId
 }
+
+class JavaBase64 : Base64 {
+    override fun encode(input: ByteArray): String {
+        return java.util.Base64.getEncoder().encode(input).toString(Charsets.UTF_8)
+    }
+
+    override fun decode(input: String): ByteArray {
+        return java.util.Base64.getDecoder().decode(input)
+    }
+}
\ No newline at end of file