diff --git a/impl.go b/impl.go
index 0a9906b..17b16dc 100644
--- a/impl.go
+++ b/impl.go
@@ -125,26 +125,20 @@ type Pkg struct {
 	recvPkg string
 }
 
-// Spec is ast.TypeSpec with the associated comment map.
-type Spec struct {
-	*ast.TypeSpec
-	ast.CommentMap
-}
-
 // typeSpec locates the *ast.TypeSpec for type id in the import path.
-func typeSpec(path string, id string, srcDir string) (Pkg, Spec, error) {
+func typeSpec(path string, id string, srcDir string) (Pkg, *ast.TypeSpec, error) {
 	var pkg *build.Package
 	var err error
 
 	if path == "" {
 		pkg, err = build.ImportDir(srcDir, 0)
 		if err != nil {
-			return Pkg{}, Spec{}, fmt.Errorf("couldn't find package in %s: %v", srcDir, err)
+			return Pkg{}, nil, fmt.Errorf("couldn't find package in %s: %v", srcDir, err)
 		}
 	} else {
 		pkg, err = build.Import(path, srcDir, 0)
 		if err != nil {
-			return Pkg{}, Spec{}, fmt.Errorf("couldn't find package %s: %v", path, err)
+			return Pkg{}, nil, fmt.Errorf("couldn't find package %s: %v", path, err)
 		}
 	}
 
@@ -158,8 +152,6 @@ func typeSpec(path string, id string, srcDir string) (Pkg, Spec, error) {
 			continue
 		}
 
-		cmap := ast.NewCommentMap(fset, f, f.Comments)
-
 		for _, decl := range f.Decls {
 			decl, ok := decl.(*ast.GenDecl)
 			if !ok || decl.Tok != token.TYPE {
@@ -171,12 +163,11 @@ func typeSpec(path string, id string, srcDir string) (Pkg, Spec, error) {
 					continue
 				}
 				p := Pkg{Package: pkg, FileSet: fset}
-				s := Spec{TypeSpec: spec, CommentMap: cmap.Filter(decl)}
-				return p, s, nil
+				return p, spec, nil
 			}
 		}
 	}
-	return Pkg{}, Spec{}, fmt.Errorf("type %s not found in %s", id, path)
+	return Pkg{}, nil, fmt.Errorf("type %s not found in %s", id, path)
 }
 
 // gofmt pretty-prints e.
@@ -253,7 +244,7 @@ const (
 	WithoutComments EmitComments = false
 )
 
-func (p Pkg) funcsig(f *ast.Field, cmap ast.CommentMap, comments EmitComments) Func {
+func (p Pkg) funcsig(f *ast.Field, comments EmitComments) Func {
 	fn := Func{Name: f.Names[0].Name}
 	typ := f.Type.(*ast.FuncType)
 	if typ.Params != nil {
@@ -273,8 +264,8 @@ func (p Pkg) funcsig(f *ast.Field, cmap ast.CommentMap, comments EmitComments) F
 			fn.Res = append(fn.Res, p.params(field)...)
 		}
 	}
-	if commentsBefore(f, cmap.Comments()) && comments == WithComments {
-		fn.Comments = flattenCommentMap(cmap)
+	if comments == WithComments && f.Doc != nil {
+		fn.Comments = flattenDocComment(f)
 	}
 	return fn
 }
@@ -328,7 +319,7 @@ func funcs(iface, srcDir, recvPkg string, comments EmitComments) ([]Func, error)
 			continue
 		}
 
-		fn := p.funcsig(fndecl, spec.CommentMap.Filter(fndecl), comments)
+		fn := p.funcsig(fndecl, comments)
 		fns = append(fns, fn)
 	}
 	return fns, nil
@@ -394,31 +385,14 @@ func validReceiver(recv string) bool {
 	return err == nil
 }
 
-// commentsBefore reports whether commentGroups precedes a field.
-func commentsBefore(field *ast.Field, cg []*ast.CommentGroup) bool {
-	if len(cg) > 0 {
-		return cg[0].Pos() < field.Pos()
-	}
-	return false
-}
-
-// flattenCommentMap flattens the comment map to a string.
-// This function must be used at the point when m is expected to have a single
-// element.
-func flattenCommentMap(m ast.CommentMap) string {
-	if len(m) != 1 {
-		panic("flattenCommentMap expects comment map of length 1")
-	}
+// flattenDocComment flattens the field doc comments to a string
+func flattenDocComment(f *ast.Field) string {
 	var result strings.Builder
-	for _, cgs := range m {
-		for _, cg := range cgs {
-			for _, c := range cg.List {
-				result.WriteString(c.Text)
-				// add an end-of-line character if this is '//'-style comment
-				if c.Text[1] == '/' {
-					result.WriteString("\n")
-				}
-			}
+	for _, c := range f.Doc.List {
+		result.WriteString(c.Text)
+		// add an end-of-line character if this is '//'-style comment
+		if c.Text[1] == '/' {
+			result.WriteString("\n")
 		}
 	}
 
diff --git a/impl_test.go b/impl_test.go
index 2c8e6a9..ffed4e4 100644
--- a/impl_test.go
+++ b/impl_test.go
@@ -77,8 +77,8 @@ func TestTypeSpec(t *testing.T) {
 			if reflect.DeepEqual(p, Pkg{}) {
 				t.Errorf("typeSpec(%q, %q).pkg=Pkg{} want non-nil", tt.path, tt.id)
 			}
-			if reflect.DeepEqual(spec, Spec{}) {
-				t.Errorf("typeSpec(%q, %q).spec=Spec{} want non-nil", tt.path, tt.id)
+			if spec == nil {
+				t.Errorf("typeSpec(%q, %q).spec=nil want non-nil", tt.path, tt.id)
 			}
 		}
 	}