diff --git a/src/go/ast/walk.go b/src/go/ast/walk.go
index ac1395fafd..9224264e29 100644
--- a/src/go/ast/walk.go
+++ b/src/go/ast/walk.go
@@ -112,11 +112,7 @@ func Walk(v Visitor, node Node) {
 
 	case *IndexExpr:
 		Walk(v, n.X)
-		// n.Index may be nil for invalid type instantiation expressions, e.g.
-		// var x T[].
-		if n.Index != nil {
-			Walk(v, n.Index)
-		}
+		Walk(v, n.Index)
 
 	case *SliceExpr:
 		Walk(v, n.X)
diff --git a/src/go/internal/typeparams/notypeparams.go b/src/go/internal/typeparams/notypeparams.go
index a8c25ac2b1..2ceafaac1c 100644
--- a/src/go/internal/typeparams/notypeparams.go
+++ b/src/go/internal/typeparams/notypeparams.go
@@ -15,8 +15,6 @@ const Enabled = false
 
 func PackExpr(list []ast.Expr) ast.Expr {
 	switch len(list) {
-	case 0:
-		return nil
 	case 1:
 		return list[0]
 	default:
diff --git a/src/go/internal/typeparams/typeparams.go b/src/go/internal/typeparams/typeparams.go
index 66f66afb28..871e95d998 100644
--- a/src/go/internal/typeparams/typeparams.go
+++ b/src/go/internal/typeparams/typeparams.go
@@ -17,7 +17,10 @@ const Enabled = true
 func PackExpr(list []ast.Expr) ast.Expr {
 	switch len(list) {
 	case 0:
-		return nil
+		// Return an empty ListExpr here, rather than nil, as IndexExpr.Index must
+		// never be nil.
+		// TODO(rFindley) would a BadExpr be more appropriate here?
+		return &ast.ListExpr{}
 	case 1:
 		return list[0]
 	default:
diff --git a/src/go/parser/parser.go b/src/go/parser/parser.go
index 36a044e3a2..3965641713 100644
--- a/src/go/parser/parser.go
+++ b/src/go/parser/parser.go
@@ -1095,6 +1095,7 @@ func (p *parser) parseChanType() *ast.ChanType {
 }
 
 func (p *parser) parseTypeInstance(typ ast.Expr) ast.Expr {
+	assert(p.parseTypeParams(), "parseTypeInstance while not parsing type params")
 	if p.trace {
 		defer un(trace(p, "TypeInstance"))
 	}