diff --git a/after/syntax/python.vim b/after/syntax/python.vim
index 9bdb07e..74ea072 100644
--- a/after/syntax/python.vim
+++ b/after/syntax/python.vim
@@ -6,8 +6,8 @@ if g:jedi#show_call_signatures > 0 && has('conceal')
     let s:ignore = s:e.'jedi.\{-}'.s:e
     exe 'syn match jediIgnore "'.s:ignore.'" contained conceal'
     setlocal conceallevel=2
-    syn match jediFatSymbol "*" contained conceal
-    syn match jediFat "\*[^*]\+\*" contained contains=jediFatSymbol
+    syn match jediFatSymbol "\*_\*" contained conceal
+    syn match jediFat "\*_\*.\{-}\*_\*" contained contains=jediFatSymbol
     syn match jediSpace "\v[ ]+( )@=" contained
     exe 'syn match jediFunction "'.s:full.'" keepend extend '
                 \ .' contains=jediIgnore,jediFat,jediSpace'
diff --git a/jedi_vim.py b/jedi_vim.py
index aee273c..3eefca2 100644
--- a/jedi_vim.py
+++ b/jedi_vim.py
@@ -283,7 +283,8 @@ def show_call_signatures(signatures=()):
 
         params = [p.description.replace('\n', '') for p in signature.params]
         try:
-            params[signature.index] = '*%s*' % params[signature.index]
+            # *_*PLACEHOLDER*_* makes something fat. See after/syntax file.
+            params[signature.index] = '*_*%s*_*' % params[signature.index]
         except (IndexError, TypeError):
             pass