diff --git a/solver/pb/proto_test.go b/solver/pb/proto_test.go
new file mode 100644
index 000000000000..09e695f2903f
--- /dev/null
+++ b/solver/pb/proto_test.go
@@ -0,0 +1,47 @@
+package pb
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/golang/protobuf/proto" //nolint:staticcheck
+)
+
+var record = flag.Bool("record", false, "record actual values as fixtures")
+
+func TestProto(t *testing.T) {
+	// Because of stable_marshaler_all, the map will be sorted in the result binary.
+	r := &SourceOp{
+		Identifier: "docker-image://docker.io/library/foo:latest",
+		Attrs: map[string]string{
+			"a": "foo",
+			"b": "bar",
+			"c": "baz",
+		},
+	}
+
+	gogo, err := r.Marshal()
+	require.NoError(t, err)
+	assertProto(t, gogo, "SourceOp")
+
+	google, err := proto.Marshal(r)
+	require.NoError(t, err)
+	assertProto(t, google, "SourceOp")
+}
+
+func assertProto(tb testing.TB, actual []byte, name string) {
+	path := fmt.Sprintf("testdata/%s.bin", name)
+	if *record {
+		err := os.WriteFile(path, actual, 0600)
+		require.NoError(tb, err)
+		return
+	}
+	expected, err := os.ReadFile(path)
+	require.NoError(tb, err)
+	assert.Equal(tb, expected, actual)
+}
diff --git a/solver/pb/testdata/SourceOp.bin b/solver/pb/testdata/SourceOp.bin
new file mode 100644
index 000000000000..c755f83af810
--- /dev/null
+++ b/solver/pb/testdata/SourceOp.bin
@@ -0,0 +1,5 @@
+
++docker-image://docker.io/library/foo:latest
+
afoo
+
bbar
+
cbaz
\ No newline at end of file