diff --git a/lib/rdoc/markdown.kpeg b/lib/rdoc/markdown.kpeg
index 576a167457..66a4aa74fd 100644
--- a/lib/rdoc/markdown.kpeg
+++ b/lib/rdoc/markdown.kpeg
@@ -530,7 +530,7 @@ AtxInline = !@Newline !(@Sp /#*/ @Sp @Newline) Inline
 AtxStart =  < /\#{1,6}/ >
             { text.length }
 
-AtxHeading = AtxStart:s @Sp AtxInline+:a (@Sp /#*/ @Sp)?  @Newline
+AtxHeading = AtxStart:s @Spacechar+ AtxInline+:a (@Sp /#*/ @Sp)?  @Newline
             { RDoc::Markup::Heading.new(s, a.join) }
 
 SetextHeading = SetextHeading1 | SetextHeading2
diff --git a/test/rdoc/test_rdoc_markdown.rb b/test/rdoc/test_rdoc_markdown.rb
index 31d5b068f9..72587caf46 100644
--- a/test/rdoc/test_rdoc_markdown.rb
+++ b/test/rdoc/test_rdoc_markdown.rb
@@ -414,10 +414,23 @@ def test_parse_escape
   end
 
   def test_parse_heading_atx
-    doc = parse "# heading\n"
+    # CommonMark Example 62
+    (1..6).each do |level|
+      doc = parse "#{"#" * level} heading\n"
+
+      expected = @RM::Document.new(
+        @RM::Heading.new(level, "heading"))
+
+      assert_equal expected, doc
+    end
+
+    # CommonMark Example 64
+    doc = parse "#5 bolt\n\n#hashtag\n"
 
     expected = @RM::Document.new(
-      @RM::Heading.new(1, "heading"))
+      para("#5 bolt"),
+      para("#hashtag"),
+    )
 
     assert_equal expected, doc
   end