diff --git a/src/go/types/call.go b/src/go/types/call.go
index 96d0429af9..16b8e4eb7c 100644
--- a/src/go/types/call.go
+++ b/src/go/types/call.go
@@ -61,7 +61,7 @@ func (check *Checker) funcInst(x *operand, ix *typeparams.IndexExpr) {
 
 	// instantiate function signature
 	res := check.Instantiate(x.Pos(), sig, targs, poslist, true).(*Signature)
-	assert(res.tparams == nil) // signature is not generic anymore
+	assert(res.TParams().Len() == 0) // signature is not generic anymore
 	if inferred {
 		check.recordInferred(ix.Orig, targs, res)
 	}
@@ -334,7 +334,7 @@ func (check *Checker) arguments(call *ast.CallExpr, sig *Signature, targs []Type
 
 		// compute result signature
 		rsig = check.Instantiate(call.Pos(), sig, targs, nil, true).(*Signature)
-		assert(rsig.tparams == nil) // signature is not generic anymore
+		assert(rsig.TParams().Len() == 0) // signature is not generic anymore
 		check.recordInferred(call, targs, rsig)
 
 		// Optimization: Only if the parameter list was adjusted do we
diff --git a/src/go/types/decl.go b/src/go/types/decl.go
index be7753d9d1..ad88c30282 100644
--- a/src/go/types/decl.go
+++ b/src/go/types/decl.go
@@ -625,7 +625,7 @@ func (check *Checker) typeDecl(obj *TypeName, tdecl *ast.TypeSpec, def *Named) {
 	named.underlying = under(named)
 
 	// If the RHS is a type parameter, it must be from this type declaration.
-	if tpar, _ := named.underlying.(*TypeParam); tpar != nil && tparamIndex(named.tparams.list(), tpar) < 0 {
+	if tpar, _ := named.underlying.(*TypeParam); tpar != nil && tparamIndex(named.TParams().list(), tpar) < 0 {
 		check.errorf(tdecl.Type, _Todo, "cannot use function type parameter %s as RHS in type declaration", tpar)
 		named.underlying = Typ[Invalid]
 	}
diff --git a/src/go/types/subst.go b/src/go/types/subst.go
index 197d79b6a8..60fc7ae819 100644
--- a/src/go/types/subst.go
+++ b/src/go/types/subst.go
@@ -193,7 +193,7 @@ func (subst *subster) typ(typ Type) Type {
 			}
 		}
 
-		if t.TParams() == nil {
+		if t.TParams().Len() == 0 {
 			dump(">>> %s is not parameterized", t)
 			return t // type is not parameterized
 		}
diff --git a/src/go/types/typestring.go b/src/go/types/typestring.go
index 18c436e3ef..6a9e7f2ac8 100644
--- a/src/go/types/typestring.go
+++ b/src/go/types/typestring.go
@@ -276,7 +276,7 @@ func writeType(buf *bytes.Buffer, typ Type, qf Qualifier, visited []Type) {
 			buf.WriteByte('[')
 			writeTypeList(buf, t.targs, qf, visited)
 			buf.WriteByte(']')
-		} else if t.TParams() != nil {
+		} else if t.TParams().Len() != 0 {
 			// parameterized type
 			writeTParamList(buf, t.TParams().list(), qf, visited)
 		}
@@ -424,7 +424,7 @@ func WriteSignature(buf *bytes.Buffer, sig *Signature, qf Qualifier) {
 }
 
 func writeSignature(buf *bytes.Buffer, sig *Signature, qf Qualifier, visited []Type) {
-	if sig.tparams != nil {
+	if sig.TParams().Len() != 0 {
 		writeTParamList(buf, sig.TParams().list(), qf, visited)
 	}