diff --git a/autoload/vimlparser.vim b/autoload/vimlparser.vim
index 9d0d9d39..12e0439d 100644
--- a/autoload/vimlparser.vim
+++ b/autoload/vimlparser.vim
@@ -1339,7 +1339,7 @@ function! s:VimLParser.parse_cmd_function()
   if left.type == s:NODE_IDENTIFIER
     let s = left.value
     let ss = split(s, '\zs')
-    if ss[0] !=# '<' && !s:isupper(ss[0]) && stridx(s, ':') == -1 && stridx(s, '#') == -1
+    if ss[0] !=# '<' && ss[0] !=# '_' && !s:isupper(ss[0]) && stridx(s, ':') == -1 && stridx(s, '#') == -1
       throw s:Err(printf('E128: Function name must start with a capital or contain a colon: %s', s), left.pos)
     endif
   endif
diff --git a/js/vimlparser.js b/js/vimlparser.js
index 908df82a..bd53510e 100644
--- a/js/vimlparser.js
+++ b/js/vimlparser.js
@@ -1622,7 +1622,7 @@ VimLParser.prototype.parse_cmd_function = function() {
     if (left.type == NODE_IDENTIFIER) {
         var s = left.value;
         var ss = viml_split(s, "\\zs");
-        if (ss[0] != "<" && !isupper(ss[0]) && viml_stridx(s, ":") == -1 && viml_stridx(s, "#") == -1) {
+        if (ss[0] != "<" && ss[0] != "_" && !isupper(ss[0]) && viml_stridx(s, ":") == -1 && viml_stridx(s, "#") == -1) {
             throw Err(viml_printf("E128: Function name must start with a capital or contain a colon: %s", s), left.pos);
         }
     }
diff --git a/py/vimlparser.py b/py/vimlparser.py
index 63c8b1a9..592f1a21 100644
--- a/py/vimlparser.py
+++ b/py/vimlparser.py
@@ -1338,7 +1338,7 @@ def parse_cmd_function(self):
         if left.type == NODE_IDENTIFIER:
             s = left.value
             ss = viml_split(s, "\\zs")
-            if ss[0] != "<" and not isupper(ss[0]) and viml_stridx(s, ":") == -1 and viml_stridx(s, "#") == -1:
+            if ss[0] != "<" and ss[0] != "_" and not isupper(ss[0]) and viml_stridx(s, ":") == -1 and viml_stridx(s, "#") == -1:
                 raise VimLParserException(Err(viml_printf("E128: Function name must start with a capital or contain a colon: %s", s), left.pos))
         # :function {name}
         if self.reader.peekn(1) != "(":
diff --git a/test/test_funcname.ok b/test/test_funcname.ok
new file mode 100644
index 00000000..d37d05ea
--- /dev/null
+++ b/test/test_funcname.ok
@@ -0,0 +1,3 @@
+(function (_F))
+(function (s:SID))
+(function (<SID>SID))
diff --git a/test/test_funcname.vim b/test/test_funcname.vim
new file mode 100644
index 00000000..b4011d27
--- /dev/null
+++ b/test/test_funcname.vim
@@ -0,0 +1,8 @@
+function _F()
+endfunction
+
+function s:SID()
+endfunction
+
+function <SID>SID()
+endfunction