diff --git a/app/src/main/java/space/hackenslacker/kanbn4droid/app/boards/BoardsRepository.kt b/app/src/main/java/space/hackenslacker/kanbn4droid/app/boards/BoardsRepository.kt
index a1b6d14..661df92 100644
--- a/app/src/main/java/space/hackenslacker/kanbn4droid/app/boards/BoardsRepository.kt
+++ b/app/src/main/java/space/hackenslacker/kanbn4droid/app/boards/BoardsRepository.kt
@@ -64,6 +64,7 @@ class BoardsRepository(
             is BoardsApiResult.Failure -> return sessionResult
         }
 
+        val previousWorkspaceId = sessionStore.getWorkspaceId()?.takeIf { it.isNotBlank() }
         sessionStore.saveWorkspaceId(normalizedWorkspaceId)
         val listBoardsResult = apiClient.listBoards(
                 baseUrl = session.baseUrl,
@@ -72,7 +73,14 @@ class BoardsRepository(
             )
         return when (listBoardsResult) {
             is BoardsApiResult.Success -> BoardsApiResult.Success(Unit)
-            is BoardsApiResult.Failure -> listBoardsResult
+            is BoardsApiResult.Failure -> {
+                if (previousWorkspaceId != null) {
+                    sessionStore.saveWorkspaceId(previousWorkspaceId)
+                } else {
+                    sessionStore.clearWorkspaceId()
+                }
+                listBoardsResult
+            }
         }
     }
 
diff --git a/app/src/main/java/space/hackenslacker/kanbn4droid/app/boards/BoardsViewModel.kt b/app/src/main/java/space/hackenslacker/kanbn4droid/app/boards/BoardsViewModel.kt
index a0eb5b5..7b85697 100644
--- a/app/src/main/java/space/hackenslacker/kanbn4droid/app/boards/BoardsViewModel.kt
+++ b/app/src/main/java/space/hackenslacker/kanbn4droid/app/boards/BoardsViewModel.kt
@@ -101,7 +101,11 @@ class BoardsViewModel(
                             ),
                         )
                     }
-                    _events.emit(BoardsUiEvent.ShowServerError(result.message))
+                    if (result.message.isUnauthorizedFailureMessage()) {
+                        _events.emit(BoardsUiEvent.ForceSignOut)
+                    } else {
+                        _events.emit(BoardsUiEvent.ShowServerError(result.message))
+                    }
                 }
             }
         }
@@ -288,3 +292,8 @@ class BoardsViewModel(
         }
     }
 }
+
+private fun String.isUnauthorizedFailureMessage(): Boolean {
+    val normalized = lowercase()
+    return "401" in normalized || "403" in normalized || "authentication" in normalized || "unauthorized" in normalized
+}
diff --git a/app/src/test/java/space/hackenslacker/kanbn4droid/app/boards/BoardsViewModelTest.kt b/app/src/test/java/space/hackenslacker/kanbn4droid/app/boards/BoardsViewModelTest.kt
index 92e0055..2905340 100644
--- a/app/src/test/java/space/hackenslacker/kanbn4droid/app/boards/BoardsViewModelTest.kt
+++ b/app/src/test/java/space/hackenslacker/kanbn4droid/app/boards/BoardsViewModelTest.kt
@@ -318,6 +318,54 @@ class BoardsViewModelTest {
         assertEquals("ws-1", sessionStore.getWorkspaceId())
     }
 
+    @Test
+    fun workspaceSwitchUnauthorizedEmitsForceSignOut() = runTest {
+        val api = FakeBoardsApiClient().apply {
+            usersMeResult = BoardsApiResult.Success(DrawerProfile(displayName = "Alice", email = null))
+            workspacesResult = BoardsApiResult.Success(
+                listOf(
+                    WorkspaceSummary("ws-1", "Main"),
+                    WorkspaceSummary("ws-2", "Platform"),
+                ),
+            )
+            listBoardsResults.addLast(BoardsApiResult.Failure("Server error: 401"))
+        }
+        val sessionStore = InMemorySessionStore("https://kan.bn/", workspaceId = "ws-1")
+        val viewModel = newViewModel(api, sessionStore = sessionStore)
+        viewModel.loadDrawerData()
+        advanceUntilIdle()
+
+        val eventDeferred = async { viewModel.events.first() }
+        viewModel.onWorkspaceSelected("ws-2")
+        advanceUntilIdle()
+
+        val event = eventDeferred.await()
+        assertTrue(event is BoardsUiEvent.ForceSignOut)
+        assertEquals("ws-1", sessionStore.getWorkspaceId())
+    }
+
+    @Test
+    fun workspaceSwitchFailureWithNullPreviousRollsBackPersistedWorkspaceId() = runTest {
+        val api = FakeBoardsApiClient().apply {
+            usersMeResult = BoardsApiResult.Success(DrawerProfile(displayName = "Alice", email = null))
+            workspacesResult = BoardsApiResult.Failure("Server error: 500")
+            listBoardsResults.addLast(BoardsApiResult.Failure("Server error: 500"))
+        }
+        val sessionStore = InMemorySessionStore("https://kan.bn/", workspaceId = null)
+        val viewModel = newViewModel(api, sessionStore = sessionStore)
+        viewModel.loadDrawerData()
+        advanceUntilIdle()
+
+        assertEquals(null, viewModel.uiState.value.drawer.activeWorkspaceId)
+        assertEquals(null, sessionStore.getWorkspaceId())
+
+        viewModel.onWorkspaceSelected("ws-2")
+        advanceUntilIdle()
+
+        assertEquals(null, sessionStore.getWorkspaceId())
+        assertEquals(null, viewModel.uiState.value.drawer.activeWorkspaceId)
+    }
+
     private fun newViewModel(
         apiClient: FakeBoardsApiClient,
         sessionStore: InMemorySessionStore = InMemorySessionStore("https://kan.bn/", workspaceId = "ws-1"),