diff --git a/src/go/types/NOTES b/src/go/types/NOTES
index 55ab4f6552..d9a5c6fc3b 100644
--- a/src/go/types/NOTES
+++ b/src/go/types/NOTES
@@ -13,6 +13,8 @@ TODO (implementation issues)
 ----------------------------------------------------------------------------------------------------
 KNOWN ISSUES
 
+- type parameter constraints are ignored when checking if a parameterized method implements the
+  matching method in an interface
 - iteration over generic variables doesn't report certain channel errors (see TODOs in code)
 - cannot handle mutually recursive parameterized interfaces using themselves as type bounds
   example: type B(type P B(P)) interface{ m() } (need to delay all checking after seting up declarations)
diff --git a/src/go/types/check_test.go b/src/go/types/check_test.go
index 0bef6014b5..1c940aa5b7 100644
--- a/src/go/types/check_test.go
+++ b/src/go/types/check_test.go
@@ -104,6 +104,7 @@ var tests = [][]string{
 	{"testdata/tmp.go2"}, // used for ad-hoc tests - file contents transient
 	{"testdata/typeargs.go2"},
 	{"testdata/typeparams.go2"},
+	{"testdata/mtypeparams.go2"},
 	{"testdata/typeinst.go2"},
 	{"testdata/typeinst2.go2"},
 	{"testdata/issues.go2"},
diff --git a/src/go/types/lookup.go b/src/go/types/lookup.go
index 47441c7ddc..21465b3d12 100644
--- a/src/go/types/lookup.go
+++ b/src/go/types/lookup.go
@@ -341,7 +341,7 @@ func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method,
 			// TODO(gri) is this always correct? what about type bounds?
 			// (Alternative is to rename/subst type parameters and compare.)
 			u := check.newUnifier(true)
-			u.x.init(mtyp.tparams)
+			u.x.init(ftyp.tparams)
 			if !u.unify(ftyp, mtyp) {
 				return m, f
 			}
@@ -414,7 +414,7 @@ func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method,
 		// TODO(gri) is this always correct? what about type bounds?
 		// (Alternative is to rename/subst type parameters and compare.)
 		u := check.newUnifier(true)
-		u.x.init(mtyp.tparams)
+		u.x.init(ftyp.tparams)
 		if !u.unify(ftyp, mtyp) {
 			return m, f
 		}
diff --git a/src/go/types/testdata/mtypeparams.go2 b/src/go/types/testdata/mtypeparams.go2
new file mode 100644
index 0000000000..6623b2f317
--- /dev/null
+++ b/src/go/types/testdata/mtypeparams.go2
@@ -0,0 +1,48 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// If types.Config.AcceptMethodTypeParams is set,
+// the type checker accepts methods that have their
+// own type parameter list.
+
+package p
+
+type S struct{}
+
+func (S) m(type T)(v T)
+
+type I interface {
+   m(type T)(v T)
+}
+
+type J interface {
+   m(type T)(v T)
+}
+
+var _ I = S{}
+var _ I = J(nil)
+
+type C interface{ n() }
+
+type Sc struct{}
+
+func (Sc) m(type T C)(v T)
+
+type Ic interface {
+   m(type T C)(v T)
+}
+
+type Jc interface {
+   m(type T C)(v T)
+}
+
+var _ Ic = Sc{}
+var _ Ic = Jc(nil)
+
+// TODO(gri) These should fail because the constraints don't match.
+var _ I = Sc{}
+var _ I = Jc(nil)
+
+var _ Ic = S{}
+var _ Ic = J(nil)
diff --git a/src/go/types/testdata/typeparams.go2 b/src/go/types/testdata/typeparams.go2
index d0ab4a87cb..ed845352cc 100644
--- a/src/go/types/testdata/typeparams.go2
+++ b/src/go/types/testdata/typeparams.go2
@@ -218,7 +218,7 @@ func init(/* ERROR func init must have no type parameters */ type P)() {}
 type T struct {}
 
 func (T) m1() {}
-// Experimental: We allow method type parameters.
+// The type checker accepts method type parameters if configured accordingly.
 func (T) m2(type)() {}
 func (T) m3(type P)() {}