diff --git a/api/go1.txt b/api/go1.txt
index 601c1f39b0..70f6feb441 100644
--- a/api/go1.txt
+++ b/api/go1.txt
@@ -2811,7 +2811,7 @@ pkg go/ast, type CompositeLit struct, Elts []Expr
 pkg go/ast, type CompositeLit struct, Lbrace token.Pos
 pkg go/ast, type CompositeLit struct, Rbrace token.Pos
 pkg go/ast, type CompositeLit struct, Type Expr
-pkg go/ast, type Decl interface { End, Pos }
+pkg go/ast, type Decl interface, unexported methods
 pkg go/ast, type Decl interface, End() token.Pos
 pkg go/ast, type Decl interface, Pos() token.Pos
 pkg go/ast, type DeclStmt struct
@@ -2824,7 +2824,7 @@ pkg go/ast, type Ellipsis struct, Ellipsis token.Pos
 pkg go/ast, type Ellipsis struct, Elt Expr
 pkg go/ast, type EmptyStmt struct
 pkg go/ast, type EmptyStmt struct, Semicolon token.Pos
-pkg go/ast, type Expr interface { End, Pos }
+pkg go/ast, type Expr interface, unexported methods
 pkg go/ast, type Expr interface, End() token.Pos
 pkg go/ast, type Expr interface, Pos() token.Pos
 pkg go/ast, type ExprStmt struct
@@ -2971,13 +2971,13 @@ pkg go/ast, type SliceExpr struct, Lbrack token.Pos
 pkg go/ast, type SliceExpr struct, Low Expr
 pkg go/ast, type SliceExpr struct, Rbrack token.Pos
 pkg go/ast, type SliceExpr struct, X Expr
-pkg go/ast, type Spec interface { End, Pos }
+pkg go/ast, type Spec interface, unexported methods
 pkg go/ast, type Spec interface, End() token.Pos
 pkg go/ast, type Spec interface, Pos() token.Pos
 pkg go/ast, type StarExpr struct
 pkg go/ast, type StarExpr struct, Star token.Pos
 pkg go/ast, type StarExpr struct, X Expr
-pkg go/ast, type Stmt interface { End, Pos }
+pkg go/ast, type Stmt interface, unexported methods
 pkg go/ast, type Stmt interface, End() token.Pos
 pkg go/ast, type Stmt interface, Pos() token.Pos
 pkg go/ast, type StructType struct
@@ -5458,7 +5458,7 @@ pkg reflect, type StructField struct, PkgPath string
 pkg reflect, type StructField struct, Tag StructTag
 pkg reflect, type StructField struct, Type Type
 pkg reflect, type StructTag string
-pkg reflect, type Type interface { Align, AssignableTo, Bits, ChanDir, Elem, Field, FieldAlign, FieldByIndex, FieldByName, FieldByNameFunc, Implements, In, IsVariadic, Key, Kind, Len, Method, MethodByName, Name, NumField, NumIn, NumMethod, NumOut, Out, PkgPath, Size, String }
+pkg reflect, type Type interface, unexported methods
 pkg reflect, type Type interface, Align() int
 pkg reflect, type Type interface, AssignableTo(Type) bool
 pkg reflect, type Type interface, Bits() int
@@ -7608,7 +7608,7 @@ pkg syscall (darwin-386), type Rlimit struct, Max uint64
 pkg syscall (darwin-386), type RouteMessage struct
 pkg syscall (darwin-386), type RouteMessage struct, Data []byte
 pkg syscall (darwin-386), type RouteMessage struct, Header RtMsghdr
-pkg syscall (darwin-386), type RoutingMessage interface {}
+pkg syscall (darwin-386), type RoutingMessage interface, unexported methods
 pkg syscall (darwin-386), type RtMetrics struct
 pkg syscall (darwin-386), type RtMetrics struct, Expire int32
 pkg syscall (darwin-386), type RtMetrics struct, Filler [4]uint32
@@ -9427,7 +9427,7 @@ pkg syscall (darwin-386-cgo), type Rlimit struct, Max uint64
 pkg syscall (darwin-386-cgo), type RouteMessage struct
 pkg syscall (darwin-386-cgo), type RouteMessage struct, Data []byte
 pkg syscall (darwin-386-cgo), type RouteMessage struct, Header RtMsghdr
-pkg syscall (darwin-386-cgo), type RoutingMessage interface {}
+pkg syscall (darwin-386-cgo), type RoutingMessage interface, unexported methods
 pkg syscall (darwin-386-cgo), type RtMetrics struct
 pkg syscall (darwin-386-cgo), type RtMetrics struct, Expire int32
 pkg syscall (darwin-386-cgo), type RtMetrics struct, Filler [4]uint32
@@ -11249,7 +11249,7 @@ pkg syscall (darwin-amd64), type Rlimit struct, Max uint64
 pkg syscall (darwin-amd64), type RouteMessage struct
 pkg syscall (darwin-amd64), type RouteMessage struct, Data []byte
 pkg syscall (darwin-amd64), type RouteMessage struct, Header RtMsghdr
-pkg syscall (darwin-amd64), type RoutingMessage interface {}
+pkg syscall (darwin-amd64), type RoutingMessage interface, unexported methods
 pkg syscall (darwin-amd64), type RtMetrics struct
 pkg syscall (darwin-amd64), type RtMetrics struct, Expire int32
 pkg syscall (darwin-amd64), type RtMetrics struct, Filler [4]uint32
@@ -13075,7 +13075,7 @@ pkg syscall (darwin-amd64-cgo), type Rlimit struct, Max uint64
 pkg syscall (darwin-amd64-cgo), type RouteMessage struct
 pkg syscall (darwin-amd64-cgo), type RouteMessage struct, Data []byte
 pkg syscall (darwin-amd64-cgo), type RouteMessage struct, Header RtMsghdr
-pkg syscall (darwin-amd64-cgo), type RoutingMessage interface {}
+pkg syscall (darwin-amd64-cgo), type RoutingMessage interface, unexported methods
 pkg syscall (darwin-amd64-cgo), type RtMetrics struct
 pkg syscall (darwin-amd64-cgo), type RtMetrics struct, Expire int32
 pkg syscall (darwin-amd64-cgo), type RtMetrics struct, Filler [4]uint32
@@ -15046,7 +15046,7 @@ pkg syscall (freebsd-386), type Rlimit struct, Max int64
 pkg syscall (freebsd-386), type RouteMessage struct
 pkg syscall (freebsd-386), type RouteMessage struct, Data []byte
 pkg syscall (freebsd-386), type RouteMessage struct, Header RtMsghdr
-pkg syscall (freebsd-386), type RoutingMessage interface {}
+pkg syscall (freebsd-386), type RoutingMessage interface, unexported methods
 pkg syscall (freebsd-386), type RtMetrics struct
 pkg syscall (freebsd-386), type RtMetrics struct, Expire uint32
 pkg syscall (freebsd-386), type RtMetrics struct, Filler [3]uint32
@@ -17022,7 +17022,7 @@ pkg syscall (freebsd-amd64), type Rlimit struct, Max int64
 pkg syscall (freebsd-amd64), type RouteMessage struct
 pkg syscall (freebsd-amd64), type RouteMessage struct, Data []byte
 pkg syscall (freebsd-amd64), type RouteMessage struct, Header RtMsghdr
-pkg syscall (freebsd-amd64), type RoutingMessage interface {}
+pkg syscall (freebsd-amd64), type RoutingMessage interface, unexported methods
 pkg syscall (freebsd-amd64), type RtMetrics struct
 pkg syscall (freebsd-amd64), type RtMetrics struct, Expire uint64
 pkg syscall (freebsd-amd64), type RtMetrics struct, Filler [3]uint64
@@ -30123,7 +30123,7 @@ pkg syscall, type RawSockaddrInet4 struct, Addr [4]byte
 pkg syscall, type RawSockaddrInet4 struct, Port uint16
 pkg syscall, type Rusage struct
 pkg syscall, type Signal int
-pkg syscall, type Sockaddr interface {}
+pkg syscall, type Sockaddr interface, unexported methods
 pkg syscall, type SockaddrInet4 struct
 pkg syscall, type SockaddrInet4 struct, Addr [4]byte
 pkg syscall, type SockaddrInet4 struct, Port int
diff --git a/src/cmd/api/goapi.go b/src/cmd/api/goapi.go
index 992762602e..a7485e0447 100644
--- a/src/cmd/api/goapi.go
+++ b/src/cmd/api/goapi.go
@@ -892,15 +892,18 @@ type method struct {
 	sig  string // "([]byte) (int, error)", from funcSigString
 }
 
-// interfaceMethods returns the expanded list of methods for an interface.
+// interfaceMethods returns the expanded list of exported methods for an interface.
+// The boolean complete reports whether the list contains all methods (that is, the
+// interface has no unexported methods).
 // pkg is the complete package name ("net/http")
 // iname is the interface name.
-func (w *Walker) interfaceMethods(pkg, iname string) (methods []method) {
+func (w *Walker) interfaceMethods(pkg, iname string) (methods []method, complete bool) {
 	t, ok := w.interfaces[pkgSymbol{pkg, iname}]
 	if !ok {
 		log.Fatalf("failed to find interface %s.%s", pkg, iname)
 	}
 
+	complete = true
 	for _, f := range t.Methods.List {
 		typ := f.Type
 		switch tv := typ.(type) {
@@ -912,6 +915,8 @@ func (w *Walker) interfaceMethods(pkg, iname string) (methods []method) {
 						name: mname.Name,
 						sig:  w.funcSigString(ft),
 					})
+				} else {
+					complete = false
 				}
 			}
 		case *ast.Ident:
@@ -927,7 +932,9 @@ func (w *Walker) interfaceMethods(pkg, iname string) (methods []method) {
 				log.Fatalf("unexported embedded interface %q in exported interface %s.%s; confused",
 					embedded, pkg, iname)
 			}
-			methods = append(methods, w.interfaceMethods(pkg, embedded)...)
+			m, c := w.interfaceMethods(pkg, embedded)
+			methods = append(methods, m...)
+			complete = complete && c
 		case *ast.SelectorExpr:
 			lhs := w.nodeString(tv.X)
 			rhs := w.nodeString(tv.Sel)
@@ -935,7 +942,9 @@ func (w *Walker) interfaceMethods(pkg, iname string) (methods []method) {
 			if !ok {
 				log.Fatalf("can't resolve selector %q in interface %s.%s", lhs, pkg, iname)
 			}
-			methods = append(methods, w.interfaceMethods(fpkg, rhs)...)
+			m, c := w.interfaceMethods(fpkg, rhs)
+			methods = append(methods, m...)
+			complete = complete && c
 		default:
 			log.Fatalf("unknown type %T in interface field", typ)
 		}
@@ -945,14 +954,28 @@ func (w *Walker) interfaceMethods(pkg, iname string) (methods []method) {
 
 func (w *Walker) walkInterfaceType(name string, t *ast.InterfaceType) {
 	methNames := []string{}
-
 	pop := w.pushScope("type " + name + " interface")
-	for _, m := range w.interfaceMethods(w.curPackageName, name) {
+	methods, complete := w.interfaceMethods(w.curPackageName, name)
+	for _, m := range methods {
 		methNames = append(methNames, m.name)
 		w.emitFeature(fmt.Sprintf("%s%s", m.name, m.sig))
 	}
+	if !complete {
+		// The method set has unexported methods, so all the
+		// implementations are provided by the same package,
+		// so the method set can be extended. Instead of recording
+		// the full set of names (below), record only that there were
+		// unexported methods. (If the interface shrinks, we will notice
+		// because a method signature emitted during the last loop,
+		// will disappear.)
+		w.emitFeature("unexported methods")
+	}
 	pop()
 
+	if !complete {
+		return
+	}
+
 	sort.Strings(methNames)
 	if len(methNames) == 0 {
 		w.emitFeature(fmt.Sprintf("type %s interface {}", name))
diff --git a/src/cmd/api/testdata/src/pkg/p1/golden.txt b/src/cmd/api/testdata/src/pkg/p1/golden.txt
index e334e5776e..180c8db434 100644
--- a/src/cmd/api/testdata/src/pkg/p1/golden.txt
+++ b/src/cmd/api/testdata/src/pkg/p1/golden.txt
@@ -37,7 +37,7 @@ pkg p1, type Embedded struct
 pkg p1, type Error interface { Error, Temporary }
 pkg p1, type Error interface, Error() string
 pkg p1, type Error interface, Temporary() bool
-pkg p1, type I interface { Get, GetNamed, Name, PackageTwoMeth, Set }
+pkg p1, type I interface, unexported methods
 pkg p1, type I interface, Get(string) int64
 pkg p1, type I interface, GetNamed(string) int64
 pkg p1, type I interface, Name() string
@@ -46,6 +46,11 @@ pkg p1, type I interface, Set(string, int64)
 pkg p1, type MyInt int
 pkg p1, type Namer interface { Name }
 pkg p1, type Namer interface, Name() string
+pkg p1, type Public interface { X, Y }
+pkg p1, type Public interface, X()
+pkg p1, type Public interface, Y()
+pkg p1, type Private interface, unexported methods
+pkg p1, type Private interface, X()
 pkg p1, type S struct
 pkg p1, type S struct, Public *int
 pkg p1, type S struct, PublicTime time.Time
diff --git a/src/cmd/api/testdata/src/pkg/p1/p1.go b/src/cmd/api/testdata/src/pkg/p1/p1.go
index d965bb75e7..412f06b615 100644
--- a/src/cmd/api/testdata/src/pkg/p1/p1.go
+++ b/src/cmd/api/testdata/src/pkg/p1/p1.go
@@ -78,6 +78,16 @@ type I interface {
 	private()
 }
 
+type Public interface {
+	X()
+	Y()
+}
+
+type Private interface {
+	X()
+	y()
+}
+
 type Error interface {
 	error
 	Temporary() bool