diff --git a/modules/mesh-build-go/cmd/mesh-build-go/archive.go b/modules/mesh-build-go/cmd/mesh-build-go/archive.go
index f8e11b65..4807201e 100644
--- a/modules/mesh-build-go/cmd/mesh-build-go/archive.go
+++ b/modules/mesh-build-go/cmd/mesh-build-go/archive.go
@@ -99,7 +99,12 @@ func (m *Module) pinnedArchive(ctx context.Context, workspace, module string, ar
 		if err != nil {
 			return nil, err
 		}
-		if err := os.WriteFile(filepath.Join(laid, art.File), body, 0o644); err != nil {
+		kept := filepath.Join(laid, art.File)
+		if err := os.WriteFile(kept, body, 0o644); err != nil {
+			return nil, err
+		}
+		// The mode is the archive's, never the account's umask: the digest is the same on every build node.
+		if err := os.Chmod(kept, 0o644); err != nil {
 			return nil, err
 		}
 	} else if err := unpackUpstream(file, laid, art.Within); err != nil {
@@ -274,6 +279,10 @@ func untar(stream io.Reader, into, within string) error {
 			if err != nil {
 				return err
 			}
+			if err := out.Chmod(mode); err != nil {
+				out.Close()
+				return err
+			}
 			if _, err := io.Copy(out, io.LimitReader(reader, header.Size)); err != nil {
 				out.Close()
 				return err
diff --git a/modules/mesh-build-go/cmd/mesh-build-go/archive_test.go b/modules/mesh-build-go/cmd/mesh-build-go/archive_test.go
index 509668ed..90d75fe4 100644
--- a/modules/mesh-build-go/cmd/mesh-build-go/archive_test.go
+++ b/modules/mesh-build-go/cmd/mesh-build-go/archive_test.go
@@ -43,7 +43,16 @@ func copyTree(t *testing.T, from, to string) {
 		if err != nil {
 			return err
 		}
-		return os.WriteFile(target, body, info.Mode().Perm())
+		// The modes a checkout gives depend on the umask of whoever checked it out; the fixture's are its executable bit
+		// alone, as git records it, so the digest does not depend on the machine the test runs on.
+		mode := os.FileMode(0o644)
+		if info.Mode().Perm()&0o100 != 0 {
+			mode = 0o755
+		}
+		if err := os.WriteFile(target, body, mode); err != nil {
+			return err
+		}
+		return os.Chmod(target, mode)
 	})
 	if err != nil {
 		t.Fatal(err)