diff --git a/src/cmd/compile/internal/walk/builtin.go b/src/cmd/compile/internal/walk/builtin.go
index 786c31313c417..0bb501825071d 100644
--- a/src/cmd/compile/internal/walk/builtin.go
+++ b/src/cmd/compile/internal/walk/builtin.go
@@ -255,7 +255,10 @@ func walkLenCap(n *ir.UnaryExpr, init *ir.Nodes) ir.Node {
 		return mkcall("countrunes", n.Type(), init, typecheck.Conv(n.X.(*ir.ConvExpr).X, types.Types[types.TSTRING]))
 	}
 	if isByteCount(n) {
-		_, len := backingArrayPtrLen(cheapExpr(n.X.(*ir.ConvExpr).X, init))
+		conv := n.X.(*ir.ConvExpr)
+		walkStmtList(conv.Init())
+		init.Append(ir.TakeInit(conv)...)
+		_, len := backingArrayPtrLen(cheapExpr(conv.X, init))
 		return len
 	}
 
diff --git a/test/fixedbugs/issue61778.go b/test/fixedbugs/issue61778.go
new file mode 100644
index 0000000000000..5055c9e6a210b
--- /dev/null
+++ b/test/fixedbugs/issue61778.go
@@ -0,0 +1,13 @@
+// compile
+
+// Copyright 2023 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 f(s []byte) {
+	switch "" {
+	case string(append(s, 'a')):
+	}
+}