diff --git a/go/internal/packagesdriver/sizes.go b/go/internal/packagesdriver/sizes.go
index ebde896d..eecf07fe 100644
--- a/go/internal/packagesdriver/sizes.go
+++ b/go/internal/packagesdriver/sizes.go
@@ -1,3 +1,8 @@
+// Copyright 2018 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 packagesdriver fetches type sizes for go/packages and go/analysis.
 package packagesdriver
 
 import (
@@ -25,18 +30,20 @@ func GetSizes(ctx context.Context, buildFlags, env []string, dir string, usesExp
 			tool = val
 		}
 	}
-	if tool != "" && tool == "off" {
-		return GetSizesGolist(ctx, buildFlags, env, dir, usesExportData)
-	}
 
 	if tool == "" {
 		var err error
 		tool, err = exec.LookPath("gopackagesdriver")
 		if err != nil {
-			return nil, nil
+			// We did not find the driver, so use "go list".
+			tool = "off"
 		}
 	}
 
+	if tool == "off" {
+		return GetSizesGolist(ctx, buildFlags, env, dir, usesExportData)
+	}
+
 	req, err := json.Marshal(struct {
 		Command    string   `json:"command"`
 		Env        []string `json:"env"`
diff --git a/go/packages/external.go b/go/packages/external.go
index a5963253..860c3ec1 100644
--- a/go/packages/external.go
+++ b/go/packages/external.go
@@ -26,7 +26,7 @@ type driverRequest struct {
 	Overlay    map[string][]byte `json:"overlay"`
 }
 
-// findExternalTool returns the file path of a tool that supplies
+// findExternalDriver returns the file path of a tool that supplies
 // the build system package structure, or "" if not found."
 // If GOPACKAGESDRIVER is set in the environment findExternalTool returns its
 // value, otherwise it searches for a binary named gopackagesdriver on the PATH.
diff --git a/go/packages/golist.go b/go/packages/golist.go
index 75eb1b23..e5551905 100644
--- a/go/packages/golist.go
+++ b/go/packages/golist.go
@@ -20,6 +20,7 @@ import (
 	"sync"
 	"time"
 
+	"golang.org/x/tools/go/internal/packagesdriver"
 	"golang.org/x/tools/internal/gopathwalk"
 	"golang.org/x/tools/internal/semver"
 )
@@ -390,15 +391,7 @@ func runNamedQueries(cfg *Config, driver driver, addPkg func(*Package), queries
 }
 
 func getSizes(cfg *Config) (types.Sizes, error) {
-	stdout, err := invokeGo(cfg, "env", "GOARCH")
-	if err != nil {
-		return nil, err
-	}
-
-	goarch := strings.TrimSpace(stdout.String())
-	// Assume "gc" because SizesFor doesn't respond to other compilers.
-	// TODO(matloob): add support for gccgo as needed.
-	return types.SizesFor("gc", goarch), nil
+	return packagesdriver.GetSizesGolist(cfg.Context, cfg.BuildFlags, cfg.Env, cfg.Dir, usesExportData(cfg))
 }
 
 // roots selects the appropriate paths to walk based on the passed-in configuration,