diff --git a/lua/cp/config.lua b/lua/cp/config.lua
index 6d00698..0a6e7e0 100644
--- a/lua/cp/config.lua
+++ b/lua/cp/config.lua
@@ -143,6 +143,19 @@ function M.setup(user_config)
   end
 
   local config = vim.tbl_deep_extend('force', M.defaults, user_config or {})
+
+  for contest_name, contest_config in pairs(config.contests) do
+    for lang_name, lang_config in pairs(contest_config) do
+      if type(lang_config) == 'table' and not lang_config.extension then
+        if lang_name == 'cpp' then
+          lang_config.extension = 'cpp'
+        elseif lang_name == 'python' then
+          lang_config.extension = 'py'
+        end
+      end
+    end
+  end
+
   return config
 end
 
diff --git a/spec/integration_spec.lua b/spec/integration_spec.lua
index bb3ac31..63be0d0 100644
--- a/spec/integration_spec.lua
+++ b/spec/integration_spec.lua
@@ -80,7 +80,6 @@ describe('cp integration', function()
           default_language = 'cpp',
           timeout_ms = 2000,
           cpp = {
-            extension = 'cpp',
             compile = { 'g++', '{source}', '-o', '{binary}' },
             run = { '{binary}' },
           },