diff --git a/go/types/goodarch.go b/go/types/goodarch.go
deleted file mode 100644
index 94824f9..0000000
--- a/go/types/goodarch.go
+++ /dev/null
@@ -1,57 +0,0 @@
-package types
-
-import (
-	"runtime"
-	"strings"
-)
-
-// Code for determining system-specific files stolen from
-// goinstall. We can't automatically generate goosList and
-// goarchList if this package is to remain goinstallable.
-
-const goosList = "darwin freebsd linux plan9 windows "
-const goarchList = "386 amd64 arm "
-
-// goodOSArch returns false if the filename contains a $GOOS or $GOARCH
-// suffix which does not match the current system.
-// The recognized filename formats are:
-//
-//     name_$(GOOS).*
-//     name_$(GOARCH).*
-//     name_$(GOOS)_$(GOARCH).*
-//
-func goodOSArch(filename string) (ok bool) {
-	if dot := strings.Index(filename, "."); dot != -1 {
-		filename = filename[:dot]
-	}
-	l := strings.Split(filename, "_")
-	n := len(l)
-	if n == 0 {
-		return true
-	}
-	if good, known := goodOS[l[n-1]]; known {
-		return good
-	}
-	if good, known := goodArch[l[n-1]]; known {
-		if !good || n < 2 {
-			return false
-		}
-		good, known = goodOS[l[n-2]]
-		return good || !known
-	}
-	return true
-}
-
-var goodOS = make(map[string]bool)
-var goodArch = make(map[string]bool)
-
-func init() {
-	goodOS = make(map[string]bool)
-	goodArch = make(map[string]bool)
-	for _, v := range strings.Fields(goosList) {
-		goodOS[v] = v == runtime.GOOS
-	}
-	for _, v := range strings.Fields(goarchList) {
-		goodArch[v] = v == runtime.GOARCH
-	}
-}
diff --git a/go/types/types.go b/go/types/types.go
index dc11adf..68c61bf 100644
--- a/go/types/types.go
+++ b/go/types/types.go
@@ -12,7 +12,6 @@ import (
 	"path/filepath"
 	"runtime"
 	"strconv"
-	"strings"
 
 	"github.com/rogpeppe/godef/go/ast"
 	"github.com/rogpeppe/godef/go/parser"
@@ -82,7 +81,16 @@ func DefaultImporter(path string, srcDir string) *ast.Package {
 	if err != nil {
 		return nil
 	}
-	pkgs, err := parser.ParseDir(FileSet, bpkg.Dir, isGoFile, 0, DefaultImportPathToName)
+	// Create a map for fast lookup of the files we want to parse
+	parseFiles := make(map[string]struct{}, len(bpkg.GoFiles))
+	for _, name := range bpkg.GoFiles {
+		parseFiles[name] = struct{}{}
+	}
+	filter := func(d os.FileInfo) bool {
+		_, found := parseFiles[d.Name()]
+		return found
+	}
+	pkgs, err := parser.ParseDir(FileSet, bpkg.Dir, filter, 0, DefaultImportPathToName)
 	if err != nil {
 		if Debug {
 			switch err := err.(type) {
@@ -112,18 +120,6 @@ func DefaultImportPathToName(path, srcDir string) (string, error) {
 	return pkg.Name, err
 }
 
-// isGoFile returns true if we will consider the file as a
-// possible candidate for parsing as part of a package.
-// Including _test.go here isn't quite right, but what
-// else can we do?
-//
-func isGoFile(d os.FileInfo) bool {
-	return strings.HasSuffix(d.Name(), ".go") &&
-		!strings.HasSuffix(d.Name(), "_test.go") &&
-		!strings.HasPrefix(d.Name(), ".") &&
-		goodOSArch(d.Name())
-}
-
 // When Debug is true, log messages will be printed.
 var Debug = false