diff --git a/runtime/autoload/dist/ft.vim b/runtime/autoload/dist/ft.vim
index 3c7d85c..6aea180 100644
--- a/runtime/autoload/dist/ft.vim
+++ b/runtime/autoload/dist/ft.vim
@@ -465,7 +465,7 @@
     # recognize Prolog by specific text in the first non-empty line
     # require a blank after the '%' because Perl uses "%list" and "%translate"
     var lnum = getline(nextnonblank(1))
-    if lnum =~ '\<prolog\>' || lnum =~ '^\s*\(%\+\(\s\|$\)\|/\*\)' || lnum =~ ':-'
+    if lnum =~ '\<prolog\>' || lnum =~ '(^\s*(:-\|%\|\/\*))\|.\s*$'
       setf prolog
     else
       exe 'setf ' .. default
diff --git a/src/testdir/test_filetype.vim b/src/testdir/test_filetype.vim
index 3b0b2e9..a410785 100644
--- a/src/testdir/test_filetype.vim
+++ b/src/testdir/test_filetype.vim
@@ -2576,4 +2576,31 @@
   filetype off
 endfunc
 
+func Test_pro_file()
+  filetype on
+
+  "Prolog
+  call writefile([':-module(test/1,'], 'Xfile.pro', 'D')
+  split Xfile.pro
+  call assert_equal('prolog', &filetype)
+  bwipe!
+
+  call writefile(['% comment'], 'Xfile.pro', 'D')
+  split Xfile.pro
+  call assert_equal('prolog', &filetype)
+  bwipe!
+
+  call writefile(['/* multiline comment'], 'Xfile.pro', 'D')
+  split Xfile.pro
+  call assert_equal('prolog', &filetype)
+  bwipe!
+
+  call writefile(['rule(test, 1.7).'], 'Xfile.pro', 'D')
+  split Xfile.pro
+  call assert_equal('prolog', &filetype)
+  bwipe!
+
+  filetype off
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/version.c b/src/version.c
index 9c076f8..aaef85f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    558,
+/**/
     557,
 /**/
     556,