diff --git a/assemblyscript/assemblyscript_test.go b/assemblyscript/assemblyscript_test.go
index a23895fc..7f10dcfe 100644
--- a/assemblyscript/assemblyscript_test.go
+++ b/assemblyscript/assemblyscript_test.go
@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	_ "embed"
+	"encoding/hex"
 	"errors"
 	"io"
 	"strings"
@@ -123,8 +124,7 @@ func TestAbort_Error(t *testing.T) {
 }
 
 func TestSeed(t *testing.T) {
-	b := []byte{0, 1, 2, 3, 4, 5, 6, 7}
-	mod, r, log := requireProxyModule(t, NewFunctionExporter(), wazero.NewModuleConfig().WithRandSource(bytes.NewReader(b)))
+	mod, r, log := requireProxyModule(t, NewFunctionExporter(), wazero.NewModuleConfig())
 	defer r.Close(testCtx)
 
 	ret, err := mod.ExportedFunction(functionSeed).Call(testCtx)
@@ -132,11 +132,11 @@ func TestSeed(t *testing.T) {
 	require.Equal(t, `
 --> proxy.seed()
 	==> env.~lib/builtins/seed()
-	<== (7.949928895127363e-275)
-<-- (7.949928895127363e-275)
+	<== (4.958153677776298e-175)
+<-- (4.958153677776298e-175)
 `, "\n"+log.String())
 
-	require.Equal(t, b, u64.LeBytes(ret[0]))
+	require.Equal(t, "538c7f96b164bf1b", hex.EncodeToString(u64.LeBytes(ret[0])))
 }
 
 func TestSeed_error(t *testing.T) {
diff --git a/config.go b/config.go
index 99bef862..cee38053 100644
--- a/config.go
+++ b/config.go
@@ -565,12 +565,15 @@ type ModuleConfig interface {
 	// See WithNanosleep
 	WithSysNanosleep() ModuleConfig
 
-	// WithRandSource configures a source of random bytes. Defaults to crypto/rand.Reader.
+	// WithRandSource configures a source of random bytes. Defaults to return a
+	// deterministic source. You might override this with crypto/rand.Reader
 	//
-	// This reader is most commonly used by the functions like "random_get" in "wasi_snapshot_preview1" or "seed" in
-	// AssemblyScript standard "env" although it could be used by functions imported from other modules.
+	// This reader is most commonly used by the functions like "random_get" in
+	// "wasi_snapshot_preview1", "seed" in AssemblyScript standard "env", and
+	// "getRandomData" when runtime.GOOS is "js".
 	//
-	// Note: The caller is responsible to close any io.Reader they supply: It is not closed on api.Module Close.
+	// Note: The caller is responsible to close any io.Reader they supply: It
+	// is not closed on api.Module Close.
 	WithRandSource(io.Reader) ModuleConfig
 }
 
diff --git a/config_test.go b/config_test.go
index a17b2711..729450fe 100644
--- a/config_test.go
+++ b/config_test.go
@@ -2,6 +2,7 @@ package wazero
 
 import (
 	"context"
+	"crypto/rand"
 	"io"
 	"io/fs"
 	"math"
@@ -479,6 +480,23 @@ func TestModuleConfig_toSysContext(t *testing.T) {
 				testFS2, // fs
 			),
 		},
+		{
+			name:  "WithRandSource",
+			input: base.WithRandSource(rand.Reader),
+			expected: requireSysContext(t,
+				math.MaxUint32, // max
+				nil,            // args
+				nil,            // environ
+				nil,            // stdin
+				nil,            // stdout
+				nil,            // stderr
+				rand.Reader,    // randSource
+				&wt, 1,         // walltime, walltimeResolution
+				&nt, 1, // nanotime, nanotimeResolution
+				nil, // nanosleep
+				nil, // fs
+			),
+		},
 	}
 
 	for _, tt := range tests {
diff --git a/internal/platform/crypto.go b/internal/platform/crypto.go
new file mode 100644
index 00000000..c141f00f
--- /dev/null
+++ b/internal/platform/crypto.go
@@ -0,0 +1,17 @@
+package platform
+
+import (
+	"io"
+	"math/rand"
+)
+
+// seed is a fixed seed value for NewFakeRandSource.
+//
+// Trivia: While arbitrary, 42 was chosen as it is the "Ultimate Answer" in
+// the Douglas Adams novel "The Hitchhiker's Guide to the Galaxy."
+const seed = int64(42)
+
+// NewFakeRandSource returns a deterministic source of random values.
+func NewFakeRandSource() io.Reader {
+	return rand.New(rand.NewSource(seed))
+}
diff --git a/internal/sys/sys.go b/internal/sys/sys.go
index 663773e0..7b1e405c 100644
--- a/internal/sys/sys.go
+++ b/internal/sys/sys.go
@@ -2,7 +2,6 @@ package sys
 
 import (
 	"context"
-	"crypto/rand"
 	"errors"
 	"fmt"
 	"io"
@@ -118,7 +117,7 @@ func (c *Context) FS(ctx context.Context) *FSContext {
 	return c.fsc
 }
 
-// RandSource is a source of random bytes and defaults to crypto/rand.Reader.
+// RandSource is a source of random bytes and defaults to a deterministic source.
 // see wazero.ModuleConfig WithRandSource
 func (c *Context) RandSource() io.Reader {
 	return c.randSource
@@ -153,8 +152,10 @@ func NewContext(
 	stdin io.Reader,
 	stdout, stderr io.Writer,
 	randSource io.Reader,
-	walltime *sys.Walltime, walltimeResolution sys.ClockResolution,
-	nanotime *sys.Nanotime, nanotimeResolution sys.ClockResolution,
+	walltime *sys.Walltime,
+	walltimeResolution sys.ClockResolution,
+	nanotime *sys.Nanotime,
+	nanotimeResolution sys.ClockResolution,
 	nanosleep *sys.Nanosleep,
 	fs fs.FS,
 ) (sysCtx *Context, err error) {
@@ -187,7 +188,7 @@ func NewContext(
 	}
 
 	if randSource == nil {
-		sysCtx.randSource = rand.Reader
+		sysCtx.randSource = platform.NewFakeRandSource()
 	} else {
 		sysCtx.randSource = randSource
 	}
diff --git a/internal/sys/sys_test.go b/internal/sys/sys_test.go
index b4fc8b5c..1779dd36 100644
--- a/internal/sys/sys_test.go
+++ b/internal/sys/sys_test.go
@@ -3,7 +3,6 @@ package sys
 import (
 	"bytes"
 	"context"
-	"crypto/rand"
 	"io"
 	"testing"
 	"time"
@@ -55,7 +54,7 @@ func TestDefaultSysContext(t *testing.T) {
 	require.Zero(t, sysCtx.Nanotime(testCtx)) // See above on functions.
 	require.Equal(t, sys.ClockResolution(1), sysCtx.NanotimeResolution())
 	require.Equal(t, &ns, sysCtx.nanosleep)
-	require.Equal(t, rand.Reader, sysCtx.RandSource())
+	require.Equal(t, platform.NewFakeRandSource(), sysCtx.RandSource())
 	require.Equal(t, NewFSContext(testfs.FS{}), sysCtx.FS(testCtx))
 }
 
diff --git a/wasi_snapshot_preview1/random_test.go b/wasi_snapshot_preview1/random_test.go
index ee778461..53b42147 100644
--- a/wasi_snapshot_preview1/random_test.go
+++ b/wasi_snapshot_preview1/random_test.go
@@ -12,8 +12,7 @@ import (
 )
 
 func Test_randomGet(t *testing.T) {
-	mod, r, log := requireProxyModule(t, wazero.NewModuleConfig().
-		WithRandSource(deterministicRandomSource()))
+	mod, r, log := requireProxyModule(t, wazero.NewModuleConfig())
 	defer r.Close(testCtx)
 
 	expectedMemory := []byte{
@@ -42,8 +41,7 @@ func Test_randomGet(t *testing.T) {
 }
 
 func Test_randomGet_Errors(t *testing.T) {
-	mod, r, log := requireProxyModule(t, wazero.NewModuleConfig().
-		WithRandSource(deterministicRandomSource()))
+	mod, r, log := requireProxyModule(t, wazero.NewModuleConfig())
 	defer r.Close(testCtx)
 
 	memorySize := mod.Memory().Size(testCtx)
diff --git a/wasi_snapshot_preview1/wasi_test.go b/wasi_snapshot_preview1/wasi_test.go
index 7f990edb..02d1843c 100644
--- a/wasi_snapshot_preview1/wasi_test.go
+++ b/wasi_snapshot_preview1/wasi_test.go
@@ -4,8 +4,6 @@ import (
 	"bytes"
 	"context"
 	_ "embed"
-	"io"
-	"math/rand"
 	"testing"
 
 	"github.com/tetratelabs/wazero"
@@ -16,12 +14,6 @@ import (
 	"github.com/tetratelabs/wazero/internal/testing/require"
 )
 
-const seed = int64(42) // fixed seed value
-
-var deterministicRandomSource = func() io.Reader {
-	return rand.New(rand.NewSource(seed))
-}
-
 // testCtx is an arbitrary, non-default context. Non-nil also prevents linter errors.
 var testCtx = context.WithValue(context.Background(), struct{}{}, "arbitrary")