diff --git a/block.go b/block.go
index 17bf17c..ba84c67 100644
--- a/block.go
+++ b/block.go
@@ -1093,14 +1093,23 @@ func blockParagraph(out *bytes.Buffer, rndr *render, data []byte) int {
 				// render the paragraph
 				renderParagraph(out, rndr, data[:prev])
 
+				// ignore leading and trailing whitespace
+				eol := i - 1
+				for prev < eol && (data[prev] == ' ' || data[prev] == '\t') {
+					prev++
+				}
+				for eol > prev && (data[eol-1] == ' ' || data[eol-1] == '\t') {
+					eol--
+				}
+
 				// render the header
-				// this ugly, convoluted closure avoids forcing variables onto the heap
+				// this ugly double closure avoids forcing variables onto the heap
 				work := func(o *bytes.Buffer, r *render, d []byte) func() bool {
 					return func() bool {
 						parseInline(o, r, d)
 						return true
 					}
-				}(out, rndr, data[prev:i-1])
+				}(out, rndr, data[prev:eol])
 				rndr.mk.Header(out, work, level, rndr.mk.Opaque)
 
 				// find the end of the underline
diff --git a/block_test.go b/block_test.go
index 57e865d..834a7e6 100644
--- a/block_test.go
+++ b/block_test.go
@@ -91,9 +91,6 @@ func TestPrefixHeaderNoExtensions(t *testing.T) {
 		"*   List\n    * Nested list\n    # Nested header\n",
 		"<ul>\n<li><p>List</p>\n\n<ul>\n<li><p>Nested list</p>\n\n" +
 			"<h1>Nested header</h1></li>\n</ul></li>\n</ul>\n",
-
-		"*   List\n    * Sublist\n    Not a header\n    ------\n",
-		"<ul>\n<li>List\n\n<ul>\n<li>Sublist\nNot a header\n------</li>\n</ul></li>\n</ul>\n",
 	}
 	doTestsBlock(t, tests, 0)
 }
@@ -154,9 +151,53 @@ func TestPrefixHeaderSpaceExtension(t *testing.T) {
 		"*   List\n    * Nested list\n    # Nested header\n",
 		"<ul>\n<li><p>List</p>\n\n<ul>\n<li><p>Nested list</p>\n\n" +
 			"<h1>Nested header</h1></li>\n</ul></li>\n</ul>\n",
-
-		"*   List\n    * Sublist\n    Not a header\n    ------\n",
-		"<ul>\n<li>List\n\n<ul>\n<li>Sublist\nNot a header\n------</li>\n</ul></li>\n</ul>\n",
 	}
 	doTestsBlock(t, tests, EXTENSION_SPACE_HEADERS)
 }
+
+func TestUnderlineHeaders(t *testing.T) {
+	var tests = []string{
+		"Header 1\n========\n",
+		"<h1>Header 1</h1>\n",
+
+		"Header 2\n--------\n",
+		"<h2>Header 2</h2>\n",
+
+		"A\n=\n",
+		"<h1>A</h1>\n",
+
+		"B\n-\n",
+		"<h2>B</h2>\n",
+
+		"Paragraph\nHeader\n=\n",
+		"<p>Paragraph</p>\n\n<h1>Header</h1>\n",
+
+		"Header\n===\nParagraph\n",
+		"<h1>Header</h1>\n\n<p>Paragraph</p>\n",
+
+		"Header\n===\nAnother header\n---\n",
+		"<h1>Header</h1>\n\n<h2>Another header</h2>\n",
+
+		"   Header\n======\n",
+		"<h1>Header</h1>\n",
+
+		"    Code\n========\n",
+		"<pre><code>Code\n</code></pre>\n\n<p>========</p>\n",
+
+		"Header with *inline*\n=====\n",
+		"<h1>Header with <em>inline</em></h1>\n",
+
+		"*   List\n    * Sublist\n    Not a header\n    ------\n",
+		"<ul>\n<li>List\n\n<ul>\n<li>Sublist\nNot a header\n------</li>\n</ul></li>\n</ul>\n",
+
+		"Paragraph\n\n\n\n\nHeader\n===\n",
+		"<p>Paragraph</p>\n\n<h1>Header</h1>\n",
+
+		"Trailing space \n====        \n\n",
+		"<h1>Trailing space</h1>\n",
+
+		"Trailing spaces\n====        \n\n",
+		"<h1>Trailing spaces</h1>\n",
+	}
+	doTestsBlock(t, tests, 0)
+}