diff --git a/src/go/types/instantiate.go b/src/go/types/instantiate.go
index 50341e064c6..8d7a9ecfb24 100644
--- a/src/go/types/instantiate.go
+++ b/src/go/types/instantiate.go
@@ -13,6 +13,19 @@ import (
 	"go/token"
 )
 
+// An Environment is an opaque type checking environment. It may be used to
+// share identical type instances across type checked packages or calls to
+// Instantiate.
+//
+// Currently, Environment is just a placeholder and has no effect on
+// instantiation.
+type Environment struct {
+	// Environment is currently un-implemented, because our instantiatedHash
+	// logic doesn't correctly handle Named type identity across multiple
+	// packages.
+	// TODO(rfindley): implement this.
+}
+
 // Instantiate instantiates the type typ with the given type arguments targs.
 // typ must be a *Named or a *Signature type, and its number of type parameters
 // must match the number of provided type arguments. The result is a new,
@@ -20,8 +33,9 @@ import (
 // *Signature). Any methods attached to a *Named are simply copied; they are
 // not instantiated.
 //
-// If check is non-nil, it will be used to de-dupe the instance against
-// previous instances with the same identity.
+// If env is non-nil, it may be used to de-dupe the instance against previous
+// instances with the same identity. This functionality is currently
+// unimplemented.
 //
 // If verify is set and constraint satisfaction fails, the returned error may
 // be of dynamic type ArgumentError indicating which type argument did not
@@ -29,8 +43,8 @@ import (
 //
 // TODO(rfindley): change this function to also return an error if lengths of
 // tparams and targs do not match.
-func Instantiate(check *Checker, typ Type, targs []Type, validate bool) (Type, error) {
-	inst := check.instance(token.NoPos, typ, targs)
+func Instantiate(env *Environment, typ Type, targs []Type, validate bool) (Type, error) {
+	inst := (*Checker)(nil).instance(token.NoPos, typ, targs)
 
 	var err error
 	if validate {
@@ -41,7 +55,7 @@ func Instantiate(check *Checker, typ Type, targs []Type, validate bool) (Type, e
 		case *Signature:
 			tparams = t.TParams().list()
 		}
-		if i, err := check.verify(token.NoPos, tparams, targs); err != nil {
+		if i, err := (*Checker)(nil).verify(token.NoPos, tparams, targs); err != nil {
 			return inst, ArgumentError{i, err}
 		}
 	}