diff --git a/app/controllers/shopkeeper_auth/sessions_controller.rb b/app/controllers/shopkeeper_auth/sessions_controller.rb
index 7758ddc..4739587 100644
--- a/app/controllers/shopkeeper_auth/sessions_controller.rb
+++ b/app/controllers/shopkeeper_auth/sessions_controller.rb
@@ -3,7 +3,10 @@ def create
     super
     return if @resource.blank?
 
-    @resource.current_platform = request.headers["source"]
+    source = request.headers["source"]
+    return if source.blank?
+
+    @resource.current_platform = source
     @resource.save!(validate: false)
   end
 
diff --git a/test/controllers/shopkeeper_auth/sessions_controller_test.rb b/test/controllers/shopkeeper_auth/sessions_controller_test.rb
index 4e9067a..5509d84 100644
--- a/test/controllers/shopkeeper_auth/sessions_controller_test.rb
+++ b/test/controllers/shopkeeper_auth/sessions_controller_test.rb
@@ -28,4 +28,29 @@ class ShopkeeperAuth::SessionsControllerTest < ActionDispatch::IntegrationTest
     delete destroy_shopkeeper_session_url, headers: shopkeeper.create_new_auth_token
     assert_response :success
   end
+
+  test "successful sign-in updates current_platform to the source header value" do
+    shopkeeper = shopkeepers(:one)
+    shopkeeper.create_default_account
+    shopkeeper.update_column(:current_platform, "ios")
+
+    post shopkeeper_session_url,
+      params: {email: shopkeeper.email, password: "password"},
+      headers: {source: "android"}
+
+    assert_response :success
+    assert_equal "android", shopkeeper.reload.current_platform
+  end
+
+  test "successful sign-in without source header preserves the existing current_platform" do
+    shopkeeper = shopkeepers(:one)
+    shopkeeper.create_default_account
+    shopkeeper.update_column(:current_platform, "ios")
+
+    post shopkeeper_session_url,
+      params: {email: shopkeeper.email, password: "password"}
+
+    assert_response :success
+    assert_equal "ios", shopkeeper.reload.current_platform
+  end
 end