diff --git a/.github/workflows/test.yaml b/.github/workflows/test.yaml
index 6c73ed2..146c7c1 100644
--- a/.github/workflows/test.yaml
+++ b/.github/workflows/test.yaml
@@ -10,7 +10,7 @@ jobs:
       - name: Setup Go
         uses: actions/setup-go@v4
         with:
-          go-version: "1.22.x"
+          go-version: "1.21.x"
       - name: Install dependencies
         run: go get .
       - name: Vet
diff --git a/go.mod b/go.mod
index e331b1d..6372916 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module github.com/restatedev/sdk-go
 
-go 1.22.0
+go 1.21.0
 
 require (
 	github.com/golang-jwt/jwt/v5 v5.2.1
diff --git a/internal/rand/rand.go b/internal/rand/rand.go
index 946d548..acc5d61 100644
--- a/internal/rand/rand.go
+++ b/internal/rand/rand.go
@@ -3,7 +3,7 @@ package rand
 import (
 	"crypto/sha256"
 	"encoding/binary"
-	"math/rand/v2"
+	"math/rand"
 
 	"github.com/google/uuid"
 )
@@ -25,10 +25,18 @@ func (r *Rand) UUID() uuid.UUID {
 	return uuid
 }
 
+func (r *Rand) Float64() float64 {
+	// use the math/rand/v2 implementation of Float64() which is more correct
+	// and also matches our TS implementation
+	return float64(r.Uint64()<<11>>11) / (1 << 53)
+}
+
 type Source struct {
 	state [4]uint64
 }
 
+var _ rand.Source64 = (*Source)(nil)
+
 func newSource(invocationID []byte) *Source {
 	hash := sha256.New()
 	hash.Write(invocationID)
@@ -43,6 +51,12 @@ func newSource(invocationID []byte) *Source {
 	}}
 }
 
+func (s *Source) Int63() int64 {
+	return int64(s.Uint64() & ((1 << 63) - 1))
+}
+
+func (s *Source) Seed(int64) {}
+
 func (s *Source) Uint64() uint64 {
 	result := rotl((s.state[0]+s.state[3]), 23) + s.state[0]
 
diff --git a/internal/rand/rand_test.go b/internal/rand/rand_test.go
index 6a91faa..46d6f39 100644
--- a/internal/rand/rand_test.go
+++ b/internal/rand/rand_test.go
@@ -2,7 +2,7 @@ package rand
 
 import (
 	"encoding/hex"
-	"math/rand/v2"
+	"math/rand"
 	"testing"
 )
 
diff --git a/reflect.go b/reflect.go
index 08a77eb..6469f0a 100644
--- a/reflect.go
+++ b/reflect.go
@@ -14,10 +14,10 @@ type serviceNamer interface {
 }
 
 var (
-	typeOfContext       = reflect.TypeFor[Context]()
-	typeOfObjectContext = reflect.TypeFor[ObjectContext]()
-	typeOfVoid          = reflect.TypeFor[Void]()
-	typeOfError         = reflect.TypeFor[error]()
+	typeOfContext       = reflect.TypeOf((*Context)(nil)).Elem()
+	typeOfObjectContext = reflect.TypeOf((*ObjectContext)(nil)).Elem()
+	typeOfVoid          = reflect.TypeOf((*Void)(nil))
+	typeOfError         = reflect.TypeOf((*error)(nil))
 )
 
 // Object converts a struct with methods into a Virtual Object where each correctly-typed