diff --git a/src/cmd/compile/internal/escape/escape.go b/src/cmd/compile/internal/escape/escape.go
index b706d7d2c8c..05bd44c35de 100644
--- a/src/cmd/compile/internal/escape/escape.go
+++ b/src/cmd/compile/internal/escape/escape.go
@@ -1295,7 +1295,7 @@ func (e *escape) newLoc(n ir.Node, transient bool) *location {
 		if n.Op() == ir.ONAME {
 			n := n.(*ir.Name)
 			if n.Curfn != e.curfn {
-				base.Fatalf("curfn mismatch: %v != %v", n.Curfn, e.curfn)
+				base.Fatalf("curfn mismatch: %v != %v for %v", n.Curfn, e.curfn, n)
 			}
 
 			if n.Opt != nil {
@@ -1308,6 +1308,9 @@ func (e *escape) newLoc(n ir.Node, transient bool) *location {
 }
 
 func (b *batch) oldLoc(n *ir.Name) *location {
+	if n.Canonical().Opt == nil {
+		base.Fatalf("%v has no location", n)
+	}
 	return n.Canonical().Opt.(*location)
 }
 
diff --git a/src/cmd/compile/internal/noder/stencil.go b/src/cmd/compile/internal/noder/stencil.go
index d60f0af548f..3ebc8dff6d8 100644
--- a/src/cmd/compile/internal/noder/stencil.go
+++ b/src/cmd/compile/internal/noder/stencil.go
@@ -667,7 +667,10 @@ func instTypeName(name string, targs []*types.Type) string {
 // result is t; otherwise the result is a new type. It deals with recursive types
 // by using TFORW types and finding partially or fully created types via sym.Def.
 func (subst *subster) typ(t *types.Type) *types.Type {
-	if !t.HasTParam() {
+	if !t.HasTParam() && t.Kind() != types.TFUNC {
+		// Note: function types need to be copied regardless, as the
+		// types of closures may contain declarations that need
+		// to be copied. See #45738.
 		return t
 	}
 
diff --git a/test/typeparam/issue45738.go b/test/typeparam/issue45738.go
new file mode 100644
index 00000000000..9f03e796a36
--- /dev/null
+++ b/test/typeparam/issue45738.go
@@ -0,0 +1,18 @@
+// compile -G=3
+
+// 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 main
+
+//go:noinline
+func f[T any]() {
+	x := 5
+	g := func() int { return x }
+	g()
+}
+
+func main() {
+	f[int]()
+}