diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 00000000..dac4b4ba
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[submodule "cardano-blueprint"]
+	path = cardano-blueprint
+	url = git@github.com:cardano-scaling/cardano-blueprint
diff --git a/cardano-blueprint b/cardano-blueprint
new file mode 160000
index 00000000..e707795c
--- /dev/null
+++ b/cardano-blueprint
@@ -0,0 +1 @@
+Subproject commit e707795ca8c82bdbe1a6c4aca6698b30503dd3b9
diff --git a/cmd/gouroboros/query.go b/cmd/gouroboros/query.go
index 7c980b10..c562ddb6 100644
--- a/cmd/gouroboros/query.go
+++ b/cmd/gouroboros/query.go
@@ -124,7 +124,9 @@ func testQuery(f *globalFlags) {
 			os.Exit(1)
 		}
 		fmt.Printf(
-			"system-start: year = %d, day = %d, picoseconds = %d\n",
+			// REVIEW: %d should work for big/Int, but warns and produces output
+			// like {%!d(bool=false) [2025]}
+			"system-start: year = %v, day = %d, picoseconds = %v\n",
 			systemStart.Year,
 			systemStart.Day,
 			systemStart.Picoseconds,
diff --git a/protocol/localstatequery/client_test.go b/protocol/localstatequery/client_test.go
index 625a4cb5..563b16e8 100644
--- a/protocol/localstatequery/client_test.go
+++ b/protocol/localstatequery/client_test.go
@@ -17,6 +17,7 @@ package localstatequery_test
 import (
 	"encoding/json"
 	"fmt"
+	"math/big"
 	"reflect"
 	"testing"
 	"time"
@@ -290,9 +291,9 @@ func TestGetUTxOByAddress(t *testing.T) {
 func TestGenesisConfigJSON(t *testing.T) {
 	genesisConfig := localstatequery.GenesisConfigResult{
 		Start: localstatequery.SystemStartResult{
-			Year:        2024,
+			Year:        *big.NewInt(2024),
 			Day:         35,
-			Picoseconds: 1234567890123456,
+			Picoseconds: *big.NewInt(1234567890123456),
 		},
 		NetworkMagic:      764824073,
 		NetworkId:         1,
diff --git a/protocol/localstatequery/messages_test.go b/protocol/localstatequery/messages_test.go
index 8538557b..5570fef3 100644
--- a/protocol/localstatequery/messages_test.go
+++ b/protocol/localstatequery/messages_test.go
@@ -16,6 +16,9 @@ package localstatequery
 
 import (
 	"encoding/hex"
+	"fmt"
+	"math/big"
+	"os"
 	"reflect"
 	"testing"
 
@@ -28,6 +31,7 @@ type testDefinition struct {
 	CborHex     string
 	Message     protocol.Message
 	MessageType uint
+	Result      interface{}
 }
 
 var tests = []testDefinition{
@@ -92,6 +96,26 @@ var tests = []testDefinition{
 		Message:     NewMsgReAcquireVolatileTip(),
 		MessageType: MessageTypeReacquireVolatileTip,
 	},
+	{
+		CborHex:     string(readFile("../../cardano-blueprint/src/api/examples/getSystemStart/query.cbor")),
+		Message:     NewMsgQuery(&SystemStartQuery{simpleQueryBase{Type: QueryTypeSystemStart}}),
+		MessageType: MessageTypeQuery,
+	},
+	{
+		CborHex: string(readFile("../../cardano-blueprint/src/api/examples/getSystemStart/result.cbor")),
+		Message: NewMsgResult(unsafeCbor(
+			SystemStartResult{
+				Year:        unsafeBigInt([]byte("703941703872597091335551638723343370661404331303175992839224705786473148")),
+				Day:         -4205646576720553090,
+				Picoseconds: unsafeBigInt([]byte("-554918151390414980540174869115975093799476848534297657333456993160799627")),
+			})),
+		MessageType: MessageTypeResult,
+		Result: SystemStartResult{
+			Year:        unsafeBigInt([]byte("703941703872597091335551638723343370661404331303175992839224705786473148")),
+			Day:         -4205646576720553090,
+			Picoseconds: unsafeBigInt([]byte("-554918151390414980540174869115975093799476848534297657333456993160799627")),
+		},
+	},
 }
 
 func TestDecode(t *testing.T) {
@@ -104,6 +128,23 @@ func TestDecode(t *testing.T) {
 		if err != nil {
 			t.Fatalf("failed to decode CBOR: %s", err)
 		}
+		// cast msg to MsgResult and further try to decode cbor
+		if m, ok := msg.(*MsgResult); ok && test.Result != nil {
+			var decoded = reflect.New(reflect.TypeOf(test.Result))
+			_, err := cbor.Decode(m.Result, decoded.Interface())
+			if err != nil {
+				t.Fatalf("failed to decode result: %s", err)
+			}
+			var actual = reflect.Indirect(decoded).Interface()
+			if !reflect.DeepEqual(actual, test.Result) {
+				t.Fatalf(
+					"MsgResult content did not decode to expected Result object\n  got:    %#v\n  wanted: %#v",
+					actual,
+					test.Result,
+				)
+			}
+		}
+
 		// Set the raw CBOR so the comparison should succeed
 		test.Message.SetCbor(cborData)
 		if m, ok := msg.(*MsgQuery); ok {
@@ -135,3 +176,30 @@ func TestEncode(t *testing.T) {
 		}
 	}
 }
+
+// Helper function to encode to cbor or panic
+func unsafeCbor(data interface{}) []byte {
+	cborData, err := cbor.Encode(data)
+	if err != nil {
+		panic(fmt.Sprintf("error encoding to CBOR: %s", err))
+	}
+	return cborData
+}
+
+func unsafeBigInt(text []byte) big.Int {
+	var i big.Int
+	err := i.UnmarshalText(text)
+	if err != nil {
+		panic(fmt.Sprintf("error unmarshalling text to big.Int: %s", err))
+	}
+	return i
+}
+
+// Helper function to allow inline reading of a file without capturing the error
+func readFile(path string) []byte {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		panic(fmt.Sprintf("error reading file: %s", err))
+	}
+	return data
+}
diff --git a/protocol/localstatequery/queries.go b/protocol/localstatequery/queries.go
index 5f017e02..f3ceaa98 100644
--- a/protocol/localstatequery/queries.go
+++ b/protocol/localstatequery/queries.go
@@ -15,7 +15,9 @@
 package localstatequery
 
 import (
+	"encoding/json"
 	"fmt"
+	"math/big"
 
 	"github.com/blinklabs-io/gouroboros/cbor"
 	"github.com/blinklabs-io/gouroboros/ledger"
@@ -416,9 +418,40 @@ type SystemStartQuery struct {
 type SystemStartResult struct {
 	// Tells the CBOR decoder to convert to/from a struct and a CBOR array
 	_           struct{} `cbor:",toarray"`
-	Year        int
+	Year        big.Int
 	Day         int
-	Picoseconds uint64
+	Picoseconds big.Int
+}
+
+func (s SystemStartResult) String() string {
+	return fmt.Sprintf("SystemStart %s %d %s", s.Year.String(), s.Day, s.Picoseconds.String())
+}
+
+func (s SystemStartResult) MarshalJSON() ([]byte, error) {
+	return json.Marshal(struct {
+		Year        string
+		Day         int
+		Picoseconds string
+	}{
+		Year:        s.Year.String(),
+		Day:         s.Day,
+		Picoseconds: s.Picoseconds.String(),
+	})
+}
+
+func (s *SystemStartResult) UnmarshalJSON(data []byte) error {
+	var tmp struct {
+		Year        string
+		Day         int
+		Picoseconds string
+	}
+	if err := json.Unmarshal(data, &tmp); err != nil {
+		return err
+	}
+	s.Year.SetString(tmp.Year, 10)
+	s.Day = tmp.Day
+	s.Picoseconds.SetString(tmp.Picoseconds, 10)
+	return nil
 }
 
 type ChainBlockNoQuery struct {