diff --git a/lib/marked.js b/lib/marked.js
index 0c2ac4b100..97f18cdb3f 100644
--- a/lib/marked.js
+++ b/lib/marked.js
@@ -456,7 +456,7 @@ var inline = {
   reflink: /^!?\[(inside)\]\s*\[([^\]]*)\]/,
   nolink: /^!?\[((?:\[[^\]]*\]|[^\[\]])*)\]/,
   strong: /^__([\s\S]+?)__(?!_)|^\*\*([\s\S]+?)\*\*(?!\*)/,
-  em: /^\b_((?:__|[\s\S])+?)_\b|^\*((?:\*\*|[\s\S])+?)\*(?!\*)/,
+  em: /^\b_((?:[^_]|__)+?)_\b|^\*((?:\*\*|[\s\S])+?)\*(?!\*)/,
   code: /^(`+)\s*([\s\S]*?[^`])\s*\1(?!`)/,
   br: /^ {2,}\n(?!\s*$)/,
   del: noop,