diff --git a/lua/opencode/ui/output_window.lua b/lua/opencode/ui/output_window.lua
index c4b98535..a9b8d0db 100644
--- a/lua/opencode/ui/output_window.lua
+++ b/lua/opencode/ui/output_window.lua
@@ -132,6 +132,11 @@ function M.update_dimensions(windows)
   if config.ui.position == 'current' then
     return
   end
+
+  if not windows or not windows.output_win or not vim.api.nvim_win_is_valid(windows.output_win) then
+    return
+  end
+
   local total_width = vim.api.nvim_get_option_value('columns', {})
 
   local width_ratio
@@ -145,8 +150,17 @@ function M.update_dimensions(windows)
   end
 
   local width = math.floor(total_width * width_ratio)
+  local ok, win_config = pcall(vim.api.nvim_win_get_config, windows.output_win)
+  if not ok then
+    return
+  end
+
+  if win_config.relative == '' then
+    pcall(vim.api.nvim_win_set_width, windows.output_win, width)
+    return
+  end
 
-  vim.api.nvim_win_set_config(windows.output_win, { width = width })
+  pcall(vim.api.nvim_win_set_config, windows.output_win, { width = width })
 end
 
 function M.get_buf_line_count()
diff --git a/lua/opencode/ui/reference_picker.lua b/lua/opencode/ui/reference_picker.lua
index 632d664f..9c618fa3 100644
--- a/lua/opencode/ui/reference_picker.lua
+++ b/lua/opencode/ui/reference_picker.lua
@@ -239,7 +239,7 @@ function M.setup()
     end)
   end
 
-  state.subscribe('messages', function()
+  state.store.subscribe('messages', function()
     M._parse_session_messages()
   end)
 end
diff --git a/tests/unit/zoom_spec.lua b/tests/unit/zoom_spec.lua
index 2ec50c6e..a6ee11ed 100644
--- a/tests/unit/zoom_spec.lua
+++ b/tests/unit/zoom_spec.lua
@@ -228,6 +228,68 @@ describe('ui zoom state', function()
 
       assert.equals(80, state.pre_zoom_width)
     end)
+
+    it('does not error when focused window is floating and output window is split', function()
+      local split_buf = vim.api.nvim_create_buf(false, true)
+      local focus_buf = vim.api.nvim_create_buf(false, true)
+      local split_win
+      local focus_win
+
+      local normal_win
+      for _, win in ipairs(vim.api.nvim_list_wins()) do
+        if vim.api.nvim_win_is_valid(win) and vim.api.nvim_win_get_config(win).relative == '' then
+          normal_win = win
+          break
+        end
+      end
+
+      assert.is_not_nil(normal_win)
+      vim.api.nvim_set_current_win(normal_win)
+      vim.cmd('vsplit')
+      split_win = vim.api.nvim_get_current_win()
+      vim.api.nvim_win_set_buf(split_win, split_buf)
+
+      focus_win = vim.api.nvim_open_win(focus_buf, true, {
+        relative = 'editor',
+        width = 20,
+        height = 5,
+        row = 1,
+        col = 1,
+        style = 'minimal',
+      })
+
+      assert.has_no.errors(function()
+        output_window.update_dimensions({ output_win = split_win, output_buf = split_buf })
+      end)
+
+      local expected_width = math.floor(config.ui.window_width * vim.o.columns)
+      assert.equals(expected_width, vim.api.nvim_win_get_width(split_win))
+
+      pcall(vim.api.nvim_win_close, focus_win, true)
+      pcall(vim.api.nvim_win_close, split_win, true)
+      pcall(vim.api.nvim_buf_delete, focus_buf, { force = true })
+      pcall(vim.api.nvim_buf_delete, split_buf, { force = true })
+    end)
+
+    it('does not error when output window is invalid', function()
+      local invalid_buf = vim.api.nvim_create_buf(false, true)
+      local invalid_win = vim.api.nvim_open_win(invalid_buf, false, {
+        relative = 'editor',
+        width = 20,
+        height = 5,
+        row = 2,
+        col = 2,
+        style = 'minimal',
+      })
+
+      vim.api.nvim_win_close(invalid_win, true)
+
+      assert.has_no.errors(function()
+        output_window.update_dimensions({ output_win = invalid_win, output_buf = invalid_buf })
+      end)
+
+      pcall(vim.api.nvim_buf_delete, invalid_buf, { force = true })
+    end)
   end)
 
   describe('zoom state persistence', function()