diff --git a/spanner/client_test.go b/spanner/client_test.go
index 4fc6219a0f4..cd29a79367c 100644
--- a/spanner/client_test.go
+++ b/spanner/client_test.go
@@ -20,6 +20,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"math/big"
 	"os"
 	"strings"
 	"testing"
@@ -2267,3 +2268,27 @@ func TestClient_DoForEachRow_ShouldEndSpanWithQueryError(t *testing.T) {
 		t.Errorf("Span status mismatch\nGot: %v\nWant: %v", s.Code, codes.InvalidArgument)
 	}
 }
+
+func TestClient_Single_Read_WithNumericKey(t *testing.T) {
+	t.Parallel()
+
+	_, client, teardown := setupMockedTestServer(t)
+	defer teardown()
+	ctx := context.Background()
+	iter := client.Single().Read(ctx, "Albums", KeySets(Key{*big.NewRat(1, 1)}), []string{"SingerId", "AlbumId", "AlbumTitle"})
+	defer iter.Stop()
+	rowCount := int64(0)
+	for {
+		_, err := iter.Next()
+		if err == iterator.Done {
+			break
+		}
+		if err != nil {
+			t.Fatal(err)
+		}
+		rowCount++
+	}
+	if rowCount != SelectSingerIDAlbumIDAlbumTitleFromAlbumsRowCount {
+		t.Fatalf("row count mismatch\nGot: %v\nWant: %v", rowCount, SelectSingerIDAlbumIDAlbumTitleFromAlbumsRowCount)
+	}
+}
diff --git a/spanner/key.go b/spanner/key.go
index d9819013bf4..aa876ec3d85 100644
--- a/spanner/key.go
+++ b/spanner/key.go
@@ -19,6 +19,7 @@ package spanner
 import (
 	"bytes"
 	"fmt"
+	"math/big"
 	"time"
 
 	"cloud.google.com/go/civil"
@@ -84,7 +85,7 @@ func keyPartValue(part interface{}) (pb *proto3.Value, err error) {
 		pb, _, err = encodeValue(int64(v))
 	case float32:
 		pb, _, err = encodeValue(float64(v))
-	case int64, float64, NullInt64, NullFloat64, bool, NullBool, []byte, string, NullString, time.Time, civil.Date, NullTime, NullDate:
+	case int64, float64, NullInt64, NullFloat64, bool, NullBool, []byte, string, NullString, time.Time, civil.Date, NullTime, NullDate, big.Rat, NullNumeric:
 		pb, _, err = encodeValue(v)
 	case Encoder:
 		part, err = v.EncodeSpanner()
@@ -150,7 +151,7 @@ func (key Key) elemString(b *bytes.Buffer, part interface{}) {
 		} else {
 			fmt.Fprint(b, nullString)
 		}
-	case NullInt64, NullFloat64, NullBool:
+	case NullInt64, NullFloat64, NullBool, NullNumeric:
 		// The above types implement fmt.Stringer.
 		fmt.Fprintf(b, "%s", v)
 	case NullString, NullDate, NullTime:
@@ -164,6 +165,8 @@ func (key Key) elemString(b *bytes.Buffer, part interface{}) {
 		fmt.Fprintf(b, "%q", v)
 	case time.Time:
 		fmt.Fprintf(b, "%q", v.Format(time.RFC3339Nano))
+	case big.Rat:
+		fmt.Fprintf(b, "%v", NumericString(&v))
 	case Encoder:
 		var err error
 		part, err = v.EncodeSpanner()
diff --git a/spanner/key_test.go b/spanner/key_test.go
index 0d5723e17a2..da103fde95e 100644
--- a/spanner/key_test.go
+++ b/spanner/key_test.go
@@ -18,6 +18,7 @@ package spanner
 
 import (
 	"errors"
+	"math/big"
 	"testing"
 	"time"
 
@@ -132,6 +133,11 @@ func TestKey(t *testing.T) {
 			wantProto: listValueProto(stringProto("2016-11-15")),
 			wantStr:   `("2016-11-15")`,
 		},
+		{
+			k:         Key{*big.NewRat(1, 1)},
+			wantProto: listValueProto(stringProto("1.000000000")),
+			wantStr:   `(1.000000000)`,
+		},
 		{
 			k:         Key{[]byte("value")},
 			wantProto: listValueProto(bytesProto([]byte("value"))),
@@ -203,6 +209,16 @@ func TestKey(t *testing.T) {
 			wantProto: listValueProto(stringProto("1"), nullProto(), stringProto("value"), floatProto(1.5), boolProto(true)),
 			wantStr:   `(1,<null>,"value",1.5,true)`,
 		},
+		{
+			k:         Key{NullNumeric{*big.NewRat(2, 3), true}},
+			wantProto: listValueProto(stringProto("0.666666667")),
+			wantStr:   "(0.666666667)",
+		},
+		{
+			k:         Key{NullNumeric{big.Rat{}, false}},
+			wantProto: listValueProto(nullProto()),
+			wantStr:   "(<null>)",
+		},
 		{
 			k:         Key{customKeyToString("value")},
 			wantProto: listValueProto(stringProto("value")),