diff --git a/src/cmd/compile/internal/types2/decl.go b/src/cmd/compile/internal/types2/decl.go
index d5495304fa3..d61d2a8b0d9 100644
--- a/src/cmd/compile/internal/types2/decl.go
+++ b/src/cmd/compile/internal/types2/decl.go
@@ -657,33 +657,24 @@ func (check *Checker) collectTypeParams(dst **TypeParamList, list []*syntax.Fiel
 	// Keep track of bounds for later validation.
 	var bound Type
 	var bounds []Type
-	var posers []poser
 	for i, f := range list {
 		// Optimization: Re-use the previous type bound if it hasn't changed.
 		// This also preserves the grouped output of type parameter lists
 		// when printing type strings.
 		if i == 0 || f.Type != list[i-1].Type {
 			bound = check.bound(f.Type)
-			bounds = append(bounds, bound)
-			posers = append(posers, f.Type)
-		}
-		tparams[i].bound = bound
-	}
-
-	check.later(func() {
-		for i, bound := range bounds {
 			if isTypeParam(bound) {
 				// We may be able to allow this since it is now well-defined what
 				// the underlying type and thus type set of a type parameter is.
 				// But we may need some additional form of cycle detection within
 				// type parameter lists.
-				check.error(posers[i], "cannot use a type parameter as constraint")
+				check.error(f.Type, "cannot use a type parameter as constraint")
+				bound = Typ[Invalid]
 			}
+			bounds = append(bounds, bound)
 		}
-		for _, tpar := range tparams {
-			tpar.iface() // compute type set
-		}
-	})
+		tparams[i].bound = bound
+	}
 }
 
 func (check *Checker) bound(x syntax.Expr) Type {
diff --git a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue50321.go2 b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue50321.go2
new file mode 100644
index 00000000000..199e66eb6ca
--- /dev/null
+++ b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue50321.go2
@@ -0,0 +1,8 @@
+// Copyright 2021 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.
+
+package p
+
+func Ln[A A /* ERROR cannot use a type parameter as constraint */ ](p A) {
+}
diff --git a/src/go/types/decl.go b/src/go/types/decl.go
index db29f11920a..02af0d5f3ea 100644
--- a/src/go/types/decl.go
+++ b/src/go/types/decl.go
@@ -708,34 +708,29 @@ func (check *Checker) collectTypeParams(dst **TypeParamList, list *ast.FieldList
 
 	index := 0
 	var bounds []Type
-	var posns []positioner // bound positions
 	for _, f := range list.List {
-		// TODO(rfindley) we should be able to rely on f.Type != nil at this point
+		var bound Type
+		// NOTE: we may be able to assert that f.Type != nil here, but this is not
+		// an invariant of the AST, so we are cautious.
 		if f.Type != nil {
-			bound := check.bound(f.Type)
-			bounds = append(bounds, bound)
-			posns = append(posns, f.Type)
-			for i := range f.Names {
-				tparams[index+i].bound = bound
-			}
-		}
-		index += len(f.Names)
-	}
-
-	check.later(func() {
-		for i, bound := range bounds {
+			bound = check.bound(f.Type)
 			if isTypeParam(bound) {
 				// We may be able to allow this since it is now well-defined what
 				// the underlying type and thus type set of a type parameter is.
 				// But we may need some additional form of cycle detection within
 				// type parameter lists.
-				check.error(posns[i], _MisplacedTypeParam, "cannot use a type parameter as constraint")
+				check.error(f.Type, _MisplacedTypeParam, "cannot use a type parameter as constraint")
+				bound = Typ[Invalid]
 			}
+		} else {
+			bound = Typ[Invalid]
 		}
-		for _, tpar := range tparams {
-			tpar.iface() // compute type set
+		bounds = append(bounds, bound)
+		for i := range f.Names {
+			tparams[index+i].bound = bound
 		}
-	})
+		index += len(f.Names)
+	}
 }
 
 func (check *Checker) bound(x ast.Expr) Type {
diff --git a/src/go/types/testdata/fixedbugs/issue50321.go2 b/src/go/types/testdata/fixedbugs/issue50321.go2
new file mode 100644
index 00000000000..199e66eb6ca
--- /dev/null
+++ b/src/go/types/testdata/fixedbugs/issue50321.go2
@@ -0,0 +1,8 @@
+// Copyright 2021 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.
+
+package p
+
+func Ln[A A /* ERROR cannot use a type parameter as constraint */ ](p A) {
+}