diff --git a/app/models/language.rb b/app/models/language.rb
--- a/app/models/language.rb
+++ b/app/models/language.rb
@@ -1,2 +1,24 @@
 class Language < ActiveRecord::Base
+
+  @@languages_by_ext = {}
+
+  def self.cache_ext_hash
+    @@languages_by_ext = {}
+    Language.find(:all).each do |language|
+      language.common_ext.split(',').each do |ext|
+        @@languages_by_ext[ext] = language
+      end
+    end
+  end
+
+  def self.find_by_extension(ext)
+    if @@languages_by_ext.length == 0
+      Language.cache_ext_hash
+    end
+    if @@languages_by_ext.has_key? ext
+      return @@languages_by_ext[ext]
+    else
+      return nil
+    end
+  end
 end
diff --git a/app/models/submission.rb b/app/models/submission.rb
--- a/app/models/submission.rb
+++ b/app/models/submission.rb
@@ -81,14 +81,17 @@
     return nil
   end
 
-  def self.find_language_in_source(source)
+  def self.find_language_in_source(source, source_filename="")
     langopt = find_option_in_source(/^LANG:/,source)
-    if language = Language.find_by_name(langopt)
-      return language
-    elsif language = Language.find_by_pretty_name(langopt)
-      return language
+    if langopt
+      return (Language.find_by_name(langopt) || 
+              Language.find_by_pretty_name(langopt))
     else
-      return nil
+      if source_filename
+        return Language.find_by_extension(source_filename.split('.').last)
+      else
+        return nil
+      end
     end
   end
 
@@ -114,7 +117,8 @@
   end
 
   def assign_language
-    self.language = Submission.find_language_in_source(self.source)
+    self.language = Submission.find_language_in_source(self.source,
+                                                       self.source_filename)
   end
 
   # validation codes
diff --git a/db/migrate/20090416235658_add_common_ext_to_languages.rb b/db/migrate/20090416235658_add_common_ext_to_languages.rb
new file mode 100644
--- /dev/null
+++ b/db/migrate/20090416235658_add_common_ext_to_languages.rb
@@ -0,0 +1,23 @@
+class AddCommonExtToLanguages < ActiveRecord::Migration
+  def self.up
+    # language.common_ext is a comma-separated list of common file
+    # extensions.
+    add_column :languages, :common_ext, :string
+
+    # updating table information
+    Language.reset_column_information
+    common_ext = { 
+      'c' => 'c',
+      'cpp' => 'cpp,cc',
+      'pas' => 'pas' 
+    }
+    Language.find(:all).each do |lang|
+      lang.common_ext = common_ext[lang.name]
+      lang.save
+    end
+  end
+
+  def self.down
+    remove_column :languages, :common_ext
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -9,7 +9,7 @@
 #
 # It's strongly recommended to check this file into your version control system.
 
-ActiveRecord::Schema.define(:version => 20090206145016) do
+ActiveRecord::Schema.define(:version => 20090416235658) do
 
   create_table "announcements", :force => true do |t|
     t.string   "author"
@@ -59,6 +59,7 @@
     t.string "name",        :limit => 10
     t.string "pretty_name"
     t.string "ext",         :limit => 10
+    t.string "common_ext"
   end
 
   create_table "messages", :force => true do |t|