diff --git a/markdown/extensions/fenced_code.py b/markdown/extensions/fenced_code.py
index 8c9935e8b..277bac405 100644
--- a/markdown/extensions/fenced_code.py
+++ b/markdown/extensions/fenced_code.py
@@ -37,7 +37,7 @@ def extendMarkdown(self, md, md_globals):
 class FencedBlockPreprocessor(Preprocessor):
     FENCED_BLOCK_RE = re.compile(r'''
 (?P<fence>^(?:~{3,}|`{3,}))[ ]*         # Opening ``` or ~~~
-(\{?\.?(?P<lang>[a-zA-Z0-9_+-]*))?[ ]*  # Optional {, and lang
+(\{?\.?(?P<lang>[\w#.+-]*))?[ ]*        # Optional {, and lang
 # Optional highlight lines, single- or double-quote-delimited
 (hl_lines=(?P<quot>"|')(?P<hl_lines>.*?)(?P=quot))?[ ]*
 }?[ ]*\n                                # Optional closing }