diff --git a/encode.go b/encode.go
index 7925941..afc35ed 100644
--- a/encode.go
+++ b/encode.go
@@ -5,6 +5,7 @@ import (
 	"encoding/binary"
 	"fmt"
 	"io"
+	"math"
 )
 
 // Encoder writes BSON values to an output stream.
@@ -64,6 +65,11 @@ func (e *Encoder) marshal(v any) error {
 		binary.LittleEndian.PutUint64(b[:], uint64(v))
 		e.buf.Write(b[:])
 
+	case float64:
+		var b [8]byte
+		binary.LittleEndian.PutUint64(b[:], math.Float64bits(float64(v)))
+		e.buf.Write(b[:])
+
 	case bool:
 		var b [1]byte
 		if v {
diff --git a/encode_test.go b/encode_test.go
index 587bd9c..e0c2538 100644
--- a/encode_test.go
+++ b/encode_test.go
@@ -2,6 +2,7 @@ package bson
 
 import (
 	"bytes"
+	"math"
 	"testing"
 )
 
@@ -56,3 +57,38 @@ func TestEncodeString(t *testing.T) {
 	wantBytes(t, buf.Bytes(), "0100000000")
 	buf.Reset()
 }
+
+func TestEncodeNumbers(t *testing.T) {
+	var buf bytes.Buffer
+	enc := NewEncoder(&buf)
+
+	err := enc.Encode(float64(3.14159))
+	mustOk(t, err)
+	wantBytes(t, buf.Bytes(), "6e861bf0f9210940")
+	buf.Reset()
+
+	err = enc.Encode(float64(0))
+	mustOk(t, err)
+	wantBytes(t, buf.Bytes(), "0000000000000000")
+	buf.Reset()
+
+	err = enc.Encode(math.NaN())
+	mustOk(t, err)
+	wantBytes(t, buf.Bytes(), "010000000000f87f")
+	buf.Reset()
+
+	err = enc.Encode(math.Inf(+1))
+	mustOk(t, err)
+	wantBytes(t, buf.Bytes(), "000000000000f07f")
+	buf.Reset()
+
+	err = enc.Encode(math.Inf(-1))
+	mustOk(t, err)
+	wantBytes(t, buf.Bytes(), "000000000000f0ff")
+	buf.Reset()
+
+	err = enc.Encode(42.13)
+	mustOk(t, err)
+	wantBytes(t, buf.Bytes(), "713d0ad7a3104540")
+	buf.Reset()
+}