diff --git a/Rakefile b/Rakefile
index 870de81..cbf111a 100644
--- a/Rakefile
+++ b/Rakefile
@@ -3,42 +3,45 @@ require 'rake/clean'
 require 'open3'
 
 M2C = 'gm2' # Modula-2 compiler.
-BOOT_OBJECTS = FileList['boot/*.mod']
+BOOT_OBJECTS = FileList['source/*.elna']
   .map do |source|
     Pathname.new(source).basename.sub_ext('.o')
   end
 
-def source_for_object(out_file)
-  path = Pathname.new(out_file).relative_path_from('build')
-  result = ['build/boot']
-
-  definition = File.join('boot', path.basename.sub_ext('.def'))
-  result << definition if File.exist? definition
-
-  implementation = path.sub_ext('.mod').to_path
-  implementation = File.join 'build', implementation unless File.exist? implementation
-
-  result << implementation
-end
-
 directory 'build/boot'
 directory 'build/self'
 
 CLEAN.include 'build'
 
-rule(/build\/.+\.o$/ => ->(file) { source_for_object(file) }) do |t|
+rule(/build\/boot\/.+\.o$/ => ->(file) {
+  path = Pathname.new('source') + Pathname.new(file).basename
+
+  ['build/boot', path.sub_ext('.def'), path.sub_ext('.elna')]
+}) do |t|
+  sources = t.prerequisites.filter { |f| f.end_with? '.elna' }
+
+  sh M2C, '-fmod=.elna', '-c', '-I', 'source', '-o', t.name, *sources
+end
+
+rule(/build\/self\/.+\.o$/ => ->(file) {
+  path = Pathname.new(file).relative_path_from('build')
+  result = []
+
+  result << File.join('source', path.basename.sub_ext('.def'))
+  result << File.join('build', path.sub_ext('.mod'))
+}) do |t|
   sources = t.prerequisites.filter { |f| f.end_with? '.mod' }
 
-  sh M2C, '-c', '-I', 'boot', '-o', t.name, *sources
+  sh M2C, '-c', '-I', 'source', '-o', t.name, *sources
 end
 
 rule(/build\/self\/.+\.mod$/ => [
   'build/self', 'build/boot/Compiler',
-  ->(file) { File.join('boot', Pathname.new(file).basename) }
+  ->(file) { File.join('source', Pathname.new(file).basename.sub_ext('.elna')) }
 ]) do |t|
   sources, compiler  = t.prerequisites
     .reject { |f| File.directory? f }
-    .partition { |f| f.end_with? '.mod' }
+    .partition { |f| f.end_with? '.elna' }
 
   File.open t.name, 'w' do |output|
     puts
@@ -62,16 +65,23 @@ end
   end
 
   compiler_object = compiler_binary.sub_ext('.o')
-  file compiler_object.to_path => source_for_object(compiler_object) do |t|
-    sources = t.prerequisites.filter { |f| f.end_with? '.mod' }
+end
 
-    sh M2C, '-fscaffold-main', '-c', '-I', 'boot', '-o', t.name, *sources
-  end
+file 'build/boot/Compiler.o' => ['build/boot', 'source/Compiler.elna'] do |t|
+  sources = t.prerequisites.filter { |f| f.end_with? '.elna' }
+
+  sh M2C, '-fscaffold-main', '-fmod=.elna', '-c', '-I', 'source', '-o', t.name, *sources
+end
+
+file 'build/self/Compiler.o' => ['build/self/Compiler.mod'] do |t|
+  sources = t.prerequisites.filter { |f| f.end_with? '.mod' }
+
+  sh M2C, '-fscaffold-main', '-c', '-I', 'source', '-o', t.name, *sources
 end
 
 task default: 'build/self/Compiler'
 task default: 'build/self/Compiler.mod'
-task default: 'boot/Compiler.mod'
+task default: 'source/Compiler.elna'
 task :default do |t|
   exe, previous_output, source = t.prerequisites
 
diff --git a/boot/Compiler.mod b/source/Compiler.elna
similarity index 100%
rename from boot/Compiler.mod
rename to source/Compiler.elna
diff --git a/boot/Lexer.def b/source/Lexer.def
similarity index 100%
rename from boot/Lexer.def
rename to source/Lexer.def
diff --git a/boot/Lexer.mod b/source/Lexer.elna
similarity index 100%
rename from boot/Lexer.mod
rename to source/Lexer.elna
diff --git a/boot/Transpiler.def b/source/Transpiler.def
similarity index 100%
rename from boot/Transpiler.def
rename to source/Transpiler.def
diff --git a/boot/Transpiler.mod b/source/Transpiler.elna
similarity index 100%
rename from boot/Transpiler.mod
rename to source/Transpiler.elna