diff --git a/htmldoc/document.go b/htmldoc/document.go
index 5b77f35..98de6d5 100644
--- a/htmldoc/document.go
+++ b/htmldoc/document.go
@@ -39,16 +39,18 @@ func (doc *Document) Init() {
 }
 
 // Parse : Ask Document to parse its HTML file. Returns quickly if this has
-// already been done. Thread safe.
+// already been done. Thread safe. Either called when the document is tested
+// or when another document needs data from this one.
 func (doc *Document) Parse() {
-	// Parse the document
-	// Either called when the document is tested or when another document needs
-	// data from this one.
-	doc.htmlMutex.Lock() // MUTEX
+	// Only one routine may parse the doc
+	doc.htmlMutex.Lock()
+	defer doc.htmlMutex.Unlock()
+
+	// If document has already been parsed, return early.
 	if doc.htmlNode != nil {
-		doc.htmlMutex.Unlock() // MUTEX
 		return
 	}
+
 	// Open, parse, and close document
 	f, err := os.Open(doc.FilePath)
 	output.CheckErrorPanic(err)
@@ -59,7 +61,6 @@ func (doc *Document) Parse() {
 
 	doc.htmlNode = htmlNode
 	doc.parseNode(htmlNode)
-	doc.htmlMutex.Unlock() // MUTEX
 }
 
 // Internal recursive function that delves into the node tree and captures
diff --git a/htmldoc/document_test.go b/htmldoc/document_test.go
index 1aed8b6..bc9ebb4 100644
--- a/htmldoc/document_test.go
+++ b/htmldoc/document_test.go
@@ -3,6 +3,7 @@ package htmldoc
 import (
 	"github.com/daviddengcn/go-assert"
 	"testing"
+	"sync"
 )
 
 func TestDocumentParse(t *testing.T) {
@@ -16,6 +17,43 @@ func TestDocumentParse(t *testing.T) {
 	assert.Equals(t, "document first body node", nodeElem.Data, "h1")
 }
 
+func TestDocumentParseOnce(t *testing.T) {
+	// Document.Parse should only parse once, subsequent calls should return quickly
+	doc := Document{
+		FilePath: "fixtures/documents/index.html",
+	}
+	doc.Init()
+	doc.Parse()
+	// Store copy of htmlNode
+	hN := doc.htmlNode
+	doc.Parse()
+	// and assert it's the same one
+	assert.Equals(t, "htmlNode", doc.htmlNode, hN)
+}
+
+func TestDocumentParseOnceConcurrent(t *testing.T) {
+	// Document.Parse should be thread safe
+	doc := Document{
+		FilePath: "fixtures/documents/index.html",
+	}
+	doc.Init()
+	// Parse many times
+	wg := sync.WaitGroup{}
+	for i := 0; i < 320; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			doc.Parse()
+		}()
+	}
+	// Wait until all jobs done
+	wg.Wait()
+	// Assert we have something sensible by the end of this
+	nodeElem := doc.htmlNode.FirstChild.FirstChild.NextSibling.FirstChild
+	assert.Equals(t, "document first body node", nodeElem.Data, "h1")
+}
+
+
 func TestDocumentNodesOfInterest(t *testing.T) {
 	doc := Document{
 		FilePath: "fixtures/documents/nodes.htm",