diff --git a/Libraries/LibMarkdown/Heading.cpp b/Libraries/LibMarkdown/Heading.cpp
index e0374c97c9..8bee287bfe 100644
--- a/Libraries/LibMarkdown/Heading.cpp
+++ b/Libraries/LibMarkdown/Heading.cpp
@@ -67,11 +67,12 @@ OwnPtr<Heading> Heading::parse(Vector<StringView>::ConstIterator& lines)
     const StringView& line = *lines;
     size_t level;
 
-    for (level = 0; level < line.length(); level++)
+    for (level = 0; level < line.length(); level++) {
         if (line[level] != '#')
             break;
+    }
 
-    if (level >= line.length() || line[level] != ' ')
+    if (!level || level >= line.length() || line[level] != ' ')
         return nullptr;
 
     StringView title_view = line.substring_view(level + 1, line.length() - level - 1);
diff --git a/Libraries/LibMarkdown/Heading.h b/Libraries/LibMarkdown/Heading.h
index f68ebd2cd3..5628f68679 100644
--- a/Libraries/LibMarkdown/Heading.h
+++ b/Libraries/LibMarkdown/Heading.h
@@ -40,6 +40,7 @@ public:
         : m_text(move(text))
         , m_level(level)
     {
+        ASSERT(m_level > 0);
     }
     virtual ~Heading() override { }