diff --git a/internal/fetch/getters.go b/internal/fetch/getters.go
index 2471f4b..75618dc 100644
--- a/internal/fetch/getters.go
+++ b/internal/fetch/getters.go
@@ -156,23 +156,29 @@
 	return 0, errors.New("directoryModuleGetter.ZipSize unimplemented")
 }
 
-// An fsModuleGetter gets modules from a directory in the filesystem
+// An fsProxyModuleGetter gets modules from a directory in the filesystem
 // that is organized like the proxy, with paths that correspond to proxy
 // URLs. An example of such a directory is $(go env GOMODCACHE)/cache/download.
-type fsModuleGetter struct {
+type fsProxyModuleGetter struct {
 	dir string
 }
 
 // NewFSModuleGetter return a ModuleGetter that reads modules from a filesystem
 // directory organized like the proxy.
-func NewFSModuleGetter(dir string) ModuleGetter {
-	return &fsModuleGetter{dir: dir}
+func NewFSProxyModuleGetter(dir string) ModuleGetter {
+	return &fsProxyModuleGetter{dir: dir}
 }
 
 // Info returns basic information about the module.
-func (g *fsModuleGetter) Info(ctx context.Context, path, version string) (_ *proxy.VersionInfo, err error) {
-	defer derrors.Wrap(&err, "fsModuleGetter.Info(%q, %q)", path, version)
+func (g *fsProxyModuleGetter) Info(ctx context.Context, path, version string) (_ *proxy.VersionInfo, err error) {
+	defer derrors.Wrap(&err, "fsProxyModuleGetter.Info(%q, %q)", path, version)
 
+	// Check for a .zip file. Some directories in the download cache have .info and .mod files but no .zip.
+	f, err := g.openFile(path, version, "zip")
+	if err != nil {
+		return nil, err
+	}
+	f.Close()
 	data, err := g.readFile(path, version, "info")
 	if err != nil {
 		return nil, err
@@ -185,15 +191,21 @@
 }
 
 // Mod returns the contents of the module's go.mod file.
-func (g *fsModuleGetter) Mod(ctx context.Context, path, version string) (_ []byte, err error) {
-	defer derrors.Wrap(&err, "fsModuleGetter.Mod(%q, %q)", path, version)
+func (g *fsProxyModuleGetter) Mod(ctx context.Context, path, version string) (_ []byte, err error) {
+	defer derrors.Wrap(&err, "fsProxyModuleGetter.Mod(%q, %q)", path, version)
 
+	// Check that .zip is readable first.
+	f, err := g.openFile(path, version, "zip")
+	if err != nil {
+		return nil, err
+	}
+	f.Close()
 	return g.readFile(path, version, "mod")
 }
 
 // ContentDir returns an fs.FS for the module's contents.
-func (g *fsModuleGetter) ContentDir(ctx context.Context, path, version string) (_ fs.FS, err error) {
-	defer derrors.Wrap(&err, "fsModuleGetter.ContentDir(%q, %q)", path, version)
+func (g *fsProxyModuleGetter) ContentDir(ctx context.Context, path, version string) (_ fs.FS, err error) {
+	defer derrors.Wrap(&err, "fsProxyModuleGetter.ContentDir(%q, %q)", path, version)
 
 	data, err := g.readFile(path, version, "zip")
 	if err != nil {
@@ -207,16 +219,14 @@
 }
 
 // ZipSize returns the approximate size of the zip file in bytes.
-func (g *fsModuleGetter) ZipSize(ctx context.Context, path, version string) (int64, error) {
-	return 0, errors.New("fsModuleGetter.ZipSize unimplemented")
+func (g *fsProxyModuleGetter) ZipSize(ctx context.Context, path, version string) (int64, error) {
+	return 0, errors.New("fsProxyModuleGetter.ZipSize unimplemented")
 }
 
-func (g *fsModuleGetter) readFile(path, version, suffix string) (_ []byte, err error) {
-	epath, err := g.escapedPath(path, version, suffix)
-	if err != nil {
-		return nil, err
-	}
-	f, err := os.Open(epath)
+func (g *fsProxyModuleGetter) readFile(path, version, suffix string) (_ []byte, err error) {
+	defer derrors.Wrap(&err, "fsProxyModuleGetter.readFile(%q, %q, %q)", path, version, suffix)
+
+	f, err := g.openFile(path, version, suffix)
 	if err != nil {
 		return nil, err
 	}
@@ -224,7 +234,22 @@
 	return ioutil.ReadAll(f)
 }
 
-func (g *fsModuleGetter) escapedPath(modulePath, version, suffix string) (string, error) {
+func (g *fsProxyModuleGetter) openFile(path, version, suffix string) (_ *os.File, err error) {
+	epath, err := g.escapedPath(path, version, suffix)
+	if err != nil {
+		return nil, err
+	}
+	f, err := os.Open(epath)
+	if err != nil {
+		if errors.Is(err, fs.ErrNotExist) {
+			err = fmt.Errorf("%w: %v", derrors.NotFound, err)
+		}
+		return nil, err
+	}
+	return f, nil
+}
+
+func (g *fsProxyModuleGetter) escapedPath(modulePath, version, suffix string) (string, error) {
 	ep, err := module.EscapePath(modulePath)
 	if err != nil {
 		return "", fmt.Errorf("path: %v: %w", err, derrors.InvalidArgument)
diff --git a/internal/fetch/getters_test.go b/internal/fetch/getters_test.go
index dab3c5f..811843e 100644
--- a/internal/fetch/getters_test.go
+++ b/internal/fetch/getters_test.go
@@ -45,7 +45,7 @@
 			"dir/github.com/a!bc/@v/v2.3.4.zip",
 		},
 	} {
-		g := NewFSModuleGetter("dir").(*fsModuleGetter)
+		g := NewFSProxyModuleGetter("dir").(*fsProxyModuleGetter)
 		got, err := g.escapedPath(test.path, test.version, test.suffix)
 		if err != nil {
 			t.Fatal(err)
@@ -56,7 +56,7 @@
 	}
 }
 
-func TestFSGetter(t *testing.T) {
+func TestFSProxyGetter(t *testing.T) {
 	ctx := context.Background()
 	const (
 		modulePath = "github.com/jackc/pgio"
@@ -67,7 +67,7 @@
 	if err != nil {
 		t.Fatal(err)
 	}
-	g := NewFSModuleGetter("testdata/modcache")
+	g := NewFSProxyModuleGetter("testdata/modcache")
 	t.Run("info", func(t *testing.T) {
 		got, err := g.Info(ctx, modulePath, version)
 		if err != nil {
@@ -77,6 +77,10 @@
 		if !cmp.Equal(got, want) {
 			t.Errorf("got %+v, want %+v", got, want)
 		}
+
+		if _, err := g.Info(ctx, "nozip.com", version); !errors.Is(err, derrors.NotFound) {
+			t.Errorf("got %v, want NotFound", err)
+		}
 	})
 	t.Run("mod", func(t *testing.T) {
 		got, err := g.Mod(ctx, modulePath, version)
@@ -87,6 +91,10 @@
 		if !cmp.Equal(got, want) {
 			t.Errorf("got %q, want %q", got, want)
 		}
+
+		if _, err := g.Mod(ctx, "nozip.com", version); !errors.Is(err, derrors.NotFound) {
+			t.Errorf("got %v, want NotFound", err)
+		}
 	})
 	t.Run("contentdir", func(t *testing.T) {
 		fsys, err := g.ContentDir(ctx, modulePath, version)
@@ -107,5 +115,9 @@
 		if !cmp.Equal(got, want) {
 			t.Errorf("got %q, want %q", got, want)
 		}
+
+		if _, err := g.ContentDir(ctx, "nozip.com", version); !errors.Is(err, derrors.NotFound) {
+			t.Errorf("got %v, want NotFound", err)
+		}
 	})
 }
diff --git a/internal/fetch/testdata/modcache/nozip.com/@v/v1.0.0.info b/internal/fetch/testdata/modcache/nozip.com/@v/v1.0.0.info
new file mode 100644
index 0000000..2e4d188
--- /dev/null
+++ b/internal/fetch/testdata/modcache/nozip.com/@v/v1.0.0.info
@@ -0,0 +1 @@
+{"Version":"v1.0.0","Time":"2019-03-30T17:04:38Z"}
\ No newline at end of file
diff --git a/internal/fetch/testdata/modcache/nozip.com/@v/v1.0.0.mod b/internal/fetch/testdata/modcache/nozip.com/@v/v1.0.0.mod
new file mode 100644
index 0000000..c1efddd
--- /dev/null
+++ b/internal/fetch/testdata/modcache/nozip.com/@v/v1.0.0.mod
@@ -0,0 +1,3 @@
+module github.com/jackc/pgio
+
+go 1.12