diff --git a/src/pkg/go/parser/parser.go b/src/pkg/go/parser/parser.go
index e362e13a7b6..fc676de5657 100644
--- a/src/pkg/go/parser/parser.go
+++ b/src/pkg/go/parser/parser.go
@@ -267,13 +267,13 @@ func (p *parser) consumeComment() (comment *ast.Comment, endline int) {
 
 // Consume a group of adjacent comments, add it to the parser's
 // comments list, and return it together with the line at which
-// the last comment in the group ends. An empty line or non-comment
-// token terminates a comment group.
+// the last comment in the group ends. A non-comment token or n
+// empty lines terminate a comment group.
 //
-func (p *parser) consumeCommentGroup() (comments *ast.CommentGroup, endline int) {
+func (p *parser) consumeCommentGroup(n int) (comments *ast.CommentGroup, endline int) {
 	var list []*ast.Comment
 	endline = p.file.Line(p.pos)
-	for p.tok == token.COMMENT && endline+1 >= p.file.Line(p.pos) {
+	for p.tok == token.COMMENT && p.file.Line(p.pos) <= endline+n {
 		var comment *ast.Comment
 		comment, endline = p.consumeComment()
 		list = append(list, comment)
@@ -314,7 +314,7 @@ func (p *parser) next() {
 		if p.file.Line(p.pos) == line {
 			// The comment is on same line as the previous token; it
 			// cannot be a lead comment but may be a line comment.
-			comment, endline = p.consumeCommentGroup()
+			comment, endline = p.consumeCommentGroup(0)
 			if p.file.Line(p.pos) != endline {
 				// The next token is on a different line, thus
 				// the last comment group is a line comment.
@@ -325,7 +325,7 @@ func (p *parser) next() {
 		// consume successor comments, if any
 		endline = -1
 		for p.tok == token.COMMENT {
-			comment, endline = p.consumeCommentGroup()
+			comment, endline = p.consumeCommentGroup(1)
 		}
 
 		if endline+1 == p.file.Line(p.pos) {
diff --git a/src/pkg/go/parser/parser_test.go b/src/pkg/go/parser/parser_test.go
index 5e45acd007a..7e0ae882187 100644
--- a/src/pkg/go/parser/parser_test.go
+++ b/src/pkg/go/parser/parser_test.go
@@ -5,10 +5,12 @@
 package parser
 
 import (
+	"bytes"
 	"fmt"
 	"go/ast"
 	"go/token"
 	"os"
+	"strings"
 	"testing"
 )
 
@@ -25,7 +27,7 @@ func TestParse(t *testing.T) {
 	for _, filename := range validFiles {
 		_, err := ParseFile(fset, filename, nil, DeclarationErrors)
 		if err != nil {
-			t.Errorf("ParseFile(%s): %v", filename, err)
+			t.Fatalf("ParseFile(%s): %v", filename, err)
 		}
 	}
 }
@@ -70,7 +72,7 @@ func TestParseExpr(t *testing.T) {
 	src := "a + b"
 	x, err := ParseExpr(src)
 	if err != nil {
-		t.Errorf("ParseExpr(%s): %v", src, err)
+		t.Fatalf("ParseExpr(%s): %v", src, err)
 	}
 	// sanity check
 	if _, ok := x.(*ast.BinaryExpr); !ok {
@@ -81,7 +83,7 @@ func TestParseExpr(t *testing.T) {
 	src = "a + *"
 	_, err = ParseExpr(src)
 	if err == nil {
-		t.Errorf("ParseExpr(%s): %v", src, err)
+		t.Fatalf("ParseExpr(%s): %v", src, err)
 	}
 
 	// it must not crash
@@ -93,7 +95,7 @@ func TestParseExpr(t *testing.T) {
 func TestColonEqualsScope(t *testing.T) {
 	f, err := ParseFile(fset, "", `package p; func f() { x, y, z := x, y, z }`, 0)
 	if err != nil {
-		t.Errorf("parse: %s", err)
+		t.Fatal(err)
 	}
 
 	// RHS refers to undefined globals; LHS does not.
@@ -115,7 +117,7 @@ func TestColonEqualsScope(t *testing.T) {
 func TestVarScope(t *testing.T) {
 	f, err := ParseFile(fset, "", `package p; func f() { var x, y, z = x, y, z }`, 0)
 	if err != nil {
-		t.Errorf("parse: %s", err)
+		t.Fatal(err)
 	}
 
 	// RHS refers to undefined globals; LHS does not.
@@ -177,3 +179,125 @@ func TestImports(t *testing.T) {
 		}
 	}
 }
+
+func TestCommentGroups(t *testing.T) {
+	f, err := ParseFile(fset, "", `
+package p /* 1a */ /* 1b */      /* 1c */ // 1d
+/* 2a
+*/
+// 2b
+const pi = 3.1415
+/* 3a */ // 3b
+/* 3c */ const e = 2.7182
+
+// Example from issue 3139
+func ExampleCount() {
+	fmt.Println(strings.Count("cheese", "e"))
+	fmt.Println(strings.Count("five", "")) // before & after each rune
+	// Output:
+	// 3
+	// 5
+}
+`, ParseComments)
+	if err != nil {
+		t.Fatal(err)
+	}
+	expected := [][]string{
+		{"/* 1a */", "/* 1b */", "/* 1c */", "// 1d"},
+		{"/* 2a\n*/", "// 2b"},
+		{"/* 3a */", "// 3b", "/* 3c */"},
+		{"// Example from issue 3139"},
+		{"// before & after each rune"},
+		{"// Output:", "// 3", "// 5"},
+	}
+	if len(f.Comments) != len(expected) {
+		t.Fatalf("got %d comment groups; expected %d", len(f.Comments), len(expected))
+	}
+	for i, exp := range expected {
+		got := f.Comments[i].List
+		if len(got) != len(exp) {
+			t.Errorf("got %d comments in group %d; expected %d", len(got), i, len(exp))
+			continue
+		}
+		for j, exp := range exp {
+			got := got[j].Text
+			if got != exp {
+				t.Errorf("got %q in group %d; expected %q", got, i, exp)
+			}
+		}
+	}
+}
+
+func getField(file *ast.File, fieldname string) *ast.Field {
+	parts := strings.Split(fieldname, ".")
+	for _, d := range file.Decls {
+		if d, ok := d.(*ast.GenDecl); ok && d.Tok == token.TYPE {
+			for _, s := range d.Specs {
+				if s, ok := s.(*ast.TypeSpec); ok && s.Name.Name == parts[0] {
+					if s, ok := s.Type.(*ast.StructType); ok {
+						for _, f := range s.Fields.List {
+							for _, name := range f.Names {
+								if name.Name == parts[1] {
+									return f
+								}
+							}
+						}
+					}
+				}
+			}
+		}
+	}
+	return nil
+}
+
+// Don't use ast.CommentGroup.Text() - we want to see exact comment text.
+func commentText(c *ast.CommentGroup) string {
+	var buf bytes.Buffer
+	if c != nil {
+		for _, c := range c.List {
+			buf.WriteString(c.Text)
+		}
+	}
+	return buf.String()
+}
+
+func checkFieldComments(t *testing.T, file *ast.File, fieldname, lead, line string) {
+	f := getField(file, fieldname)
+	if f == nil {
+		t.Fatalf("field not found: %s", fieldname)
+	}
+	if got := commentText(f.Doc); got != lead {
+		t.Errorf("got lead comment %q; expected %q", got, lead)
+	}
+	if got := commentText(f.Comment); got != line {
+		t.Errorf("got line comment %q; expected %q", got, line)
+	}
+}
+
+func TestLeadAndLineComments(t *testing.T) {
+	f, err := ParseFile(fset, "", `
+package p
+type T struct {
+	/* F1 lead comment */
+	//
+	F1 int  /* F1 */ // line comment
+	// F2 lead
+	// comment
+	F2 int  // F2 line comment
+	// f3 lead comment
+	f3 int  // f3 line comment
+}
+`, ParseComments)
+	if err != nil {
+		t.Fatal(err)
+	}
+	checkFieldComments(t, f, "T.F1", "/* F1 lead comment *///", "/* F1 */// line comment")
+	checkFieldComments(t, f, "T.F2", "// F2 lead// comment", "// F2 line comment")
+	checkFieldComments(t, f, "T.f3", "// f3 lead comment", "// f3 line comment")
+	ast.FileExports(f)
+	checkFieldComments(t, f, "T.F1", "/* F1 lead comment *///", "/* F1 */// line comment")
+	checkFieldComments(t, f, "T.F2", "// F2 lead// comment", "// F2 line comment")
+	if getField(f, "T.f3") != nil {
+		t.Error("not expected to find T.f3")
+	}
+}
diff --git a/src/pkg/go/printer/nodes.go b/src/pkg/go/printer/nodes.go
index 727d2a37147..f13f9a5a843 100644
--- a/src/pkg/go/printer/nodes.go
+++ b/src/pkg/go/printer/nodes.go
@@ -60,8 +60,8 @@ func (p *printer) linebreak(line, min int, ws whiteSpace, newSection bool) (prin
 
 // setComment sets g as the next comment if g != nil and if node comments
 // are enabled - this mode is used when printing source code fragments such
-// as exports only. It assumes that there are no other pending comments to
-// intersperse.
+// as exports only. It assumes that there is no pending comment in p.comments
+// and at most one pending comment in the p.comment cache.
 func (p *printer) setComment(g *ast.CommentGroup) {
 	if g == nil || !p.useNodeComments {
 		return
@@ -74,10 +74,19 @@ func (p *printer) setComment(g *ast.CommentGroup) {
 		// should never happen - handle gracefully and flush
 		// all comments up to g, ignore anything after that
 		p.flush(p.posFor(g.List[0].Pos()), token.ILLEGAL)
+		p.comments = p.comments[0:1]
+		// in debug mode, report error
+		p.internalError("setComment found pending comments")
 	}
 	p.comments[0] = g
 	p.cindex = 0
-	p.nextComment() // get comment ready for use
+	// don't overwrite any pending comment in the p.comment cache
+	// (there may be a pending comment when a line comment is
+	// immediately followed by a lead comment with no other
+	// tokens inbetween)
+	if p.commentOffset == infinity {
+		p.nextComment() // get comment ready for use
+	}
 }
 
 type exprListMode uint
diff --git a/src/pkg/strings/example_test.go b/src/pkg/strings/example_test.go
index 11417107282..733caf5f2db 100644
--- a/src/pkg/strings/example_test.go
+++ b/src/pkg/strings/example_test.go
@@ -41,7 +41,6 @@ func ExampleContainsAny() {
 func ExampleCount() {
 	fmt.Println(strings.Count("cheese", "e"))
 	fmt.Println(strings.Count("five", "")) // before & after each rune
-
 	// Output:
 	// 3
 	// 5