diff --git a/src/cmd/doc/doc_test.go b/src/cmd/doc/doc_test.go
index c0959acca1..fd2ae30827 100644
--- a/src/cmd/doc/doc_test.go
+++ b/src/cmd/doc/doc_test.go
@@ -724,6 +724,40 @@ var tests = []test{
 		},
 	},
 
+	// Merging comments with -src.
+	{
+		"merge comments with -src A",
+		[]string{"-src", p + "/merge", `A`},
+		[]string{
+			`A doc`,
+			`func A`,
+			`A comment`,
+		},
+		[]string{
+			`Package A doc`,
+			`Package B doc`,
+			`B doc`,
+			`B comment`,
+			`B doc`,
+		},
+	},
+	{
+		"merge comments with -src B",
+		[]string{"-src", p + "/merge", `B`},
+		[]string{
+			`B doc`,
+			`func B`,
+			`B comment`,
+		},
+		[]string{
+			`Package A doc`,
+			`Package B doc`,
+			`A doc`,
+			`A comment`,
+			`A doc`,
+		},
+	},
+
 	// No dups with -u. Issue 21797.
 	{
 		"case matching on, no dups",
diff --git a/src/cmd/doc/testdata/merge/aa.go b/src/cmd/doc/testdata/merge/aa.go
new file mode 100644
index 0000000000..f8ab92dfd0
--- /dev/null
+++ b/src/cmd/doc/testdata/merge/aa.go
@@ -0,0 +1,7 @@
+// Package comment A.
+package merge
+
+// A doc.
+func A() {
+	// A comment.
+}
diff --git a/src/cmd/doc/testdata/merge/bb.go b/src/cmd/doc/testdata/merge/bb.go
new file mode 100644
index 0000000000..fd8cf3c446
--- /dev/null
+++ b/src/cmd/doc/testdata/merge/bb.go
@@ -0,0 +1,7 @@
+// Package comment B.
+package merge
+
+// B doc.
+func B() {
+	// B comment.
+}
diff --git a/src/go/parser/interface.go b/src/go/parser/interface.go
index 500c98d496..54f9d7b80a 100644
--- a/src/go/parser/interface.go
+++ b/src/go/parser/interface.go
@@ -133,13 +133,7 @@ func ParseFile(fset *token.FileSet, filename string, src interface{}, mode Mode)
 // first error encountered are returned.
 //
 func ParseDir(fset *token.FileSet, path string, filter func(os.FileInfo) bool, mode Mode) (pkgs map[string]*ast.Package, first error) {
-	fd, err := os.Open(path)
-	if err != nil {
-		return nil, err
-	}
-	defer fd.Close()
-
-	list, err := fd.Readdir(-1)
+	list, err := ioutil.ReadDir(path)
 	if err != nil {
 		return nil, err
 	}