diff --git a/client/build.go b/client/build.go
index c47b2e2..ce9fc65 100644
--- a/client/build.go
+++ b/client/build.go
@@ -12,7 +12,6 @@ import (
 	"fmt"
 	"net/http"
 
-	"github.com/globalsign/mgo/bson"
 	"github.com/golang/glog"
 	"github.com/gorilla/websocket"
 	jsonresp "github.com/sylabs/json-resp"
@@ -48,7 +47,7 @@ func (c *Client) SubmitBuild(ctx context.Context, d Definition, libraryRef strin
 	err = jsonresp.ReadResponse(res.Body, &rd)
 	if err == nil {
 		glog.V(2).Infof("Build response - id: %s, wsurl: %s, libref: %s",
-			rd.ID.Hex(), rd.WSURL, rd.LibraryRef)
+			rd.ID, rd.WSURL, rd.LibraryRef)
 	}
 	return
 }
@@ -95,8 +94,8 @@ func (c *Client) StreamOutput(ctx context.Context, wsURL string) error {
 }
 
 // GetBuildStatus gets the status of a build from the Remote Build Service
-func (c *Client) GetBuildStatus(ctx context.Context, buildID bson.ObjectId) (rd ResponseData, err error) {
-	req, err := c.newRequest(http.MethodGet, "/v1/build/"+buildID.Hex(), "", nil)
+func (c *Client) GetBuildStatus(ctx context.Context, buildID string) (rd ResponseData, err error) {
+	req, err := c.newRequest(http.MethodGet, "/v1/build/"+buildID, "", nil)
 	if err != nil {
 		return
 	}
diff --git a/client/build_test.go b/client/build_test.go
index 76af699..2411e25 100644
--- a/client/build_test.go
+++ b/client/build_test.go
@@ -18,7 +18,6 @@ import (
 	"testing"
 	"time"
 
-	"github.com/globalsign/mgo/bson"
 	"github.com/gorilla/websocket"
 	jsonresp "github.com/sylabs/json-resp"
 )
@@ -48,11 +47,11 @@ func TestMain(m *testing.M) {
 	os.Exit(m.Run())
 }
 
-func newResponse(m *mockService, id bson.ObjectId, d Definition, libraryRef string) ResponseData {
+func newResponse(m *mockService, id string, d Definition, libraryRef string) ResponseData {
 	wsURL := url.URL{
 		Scheme: "ws",
 		Host:   m.httpAddr,
-		Path:   fmt.Sprintf("%s%s", wsPath, id.Hex()),
+		Path:   fmt.Sprintf("%s%s", wsPath, id),
 	}
 	libraryURL := url.URL{
 		Scheme: "http",
@@ -82,7 +81,7 @@ func (m *mockService) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 			m.t.Fatalf("failed to parse request: %v", err)
 		}
 		if m.buildResponseCode == http.StatusCreated {
-			id := bson.NewObjectId()
+			id := newObjectID()
 			if err := jsonresp.WriteResponse(w, newResponse(m, id, rd.Definition, rd.LibraryRef), m.buildResponseCode); err != nil {
 				m.t.Fatal(err)
 			}
@@ -94,11 +93,11 @@ func (m *mockService) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	} else if r.Method == http.MethodGet && strings.HasPrefix(r.RequestURI, buildPath) {
 		// Mock status endpoint
 		id := r.RequestURI[strings.LastIndexByte(r.RequestURI, '/')+1:]
-		if !bson.IsObjectIdHex(id) {
+		if id == "" {
 			m.t.Fatalf("failed to parse ID '%v'", id)
 		}
 		if m.statusResponseCode == http.StatusOK {
-			if err := jsonresp.WriteResponse(w, newResponse(m, bson.ObjectIdHex(id), Definition{}, ""), m.statusResponseCode); err != nil {
+			if err := jsonresp.WriteResponse(w, newResponse(m, id, Definition{}, ""), m.statusResponseCode); err != nil {
 				m.t.Fatal(err)
 			}
 		} else {
@@ -310,7 +309,7 @@ func TestDoBuildRequest(t *testing.T) {
 				if err != nil {
 					t.Fatalf("unexpected failure: %v", err)
 				}
-				if !rd.ID.Valid() {
+				if rd.ID == "" {
 					t.Fatalf("invalid ID")
 				}
 				if rd.WSURL == "" {
@@ -367,7 +366,7 @@ func TestDoStatusRequest(t *testing.T) {
 	}
 
 	// ID to test with
-	id := bson.NewObjectId()
+	id := newObjectID()
 
 	// Loop over test cases
 	for _, tt := range tests {
diff --git a/client/object_id_test.go b/client/object_id_test.go
new file mode 100644
index 0000000..728c8a4
--- /dev/null
+++ b/client/object_id_test.go
@@ -0,0 +1,68 @@
+// Copyright (c) 2018-2019, Sylabs Inc. All rights reserved.
+// This software is licensed under a 3-clause BSD license. Please consult the
+// LICENSE.md file distributed with the sources of this project regarding your
+// rights to use or distribute this software.
+
+package client
+
+import (
+	"crypto/md5"
+	"crypto/rand"
+	"encoding/binary"
+	"fmt"
+	"io"
+	"os"
+	"sync/atomic"
+	"time"
+)
+
+var (
+	objectIdCounter = readRandomUint32()
+	machineId       = readMachineId()
+	processId       = os.Getpid()
+)
+
+func readRandomUint32() uint32 {
+	var b [4]byte
+	_, err := io.ReadFull(rand.Reader, b[:])
+	if err != nil {
+		panic(fmt.Errorf("cannot read random object id: %v", err))
+	}
+	return uint32((uint32(b[0]) << 0) | (uint32(b[1]) << 8) | (uint32(b[2]) << 16) | (uint32(b[3]) << 24))
+}
+
+func readMachineId() []byte {
+	var sum [3]byte
+	id := sum[:]
+	hostname, err1 := os.Hostname()
+	if err1 != nil {
+		_, err2 := io.ReadFull(rand.Reader, id)
+		if err2 != nil {
+			panic(fmt.Errorf("cannot get hostname: %v; %v", err1, err2))
+		}
+		return id
+	}
+	hw := md5.New()
+	hw.Write([]byte(hostname))
+	copy(id, hw.Sum(nil))
+	return id
+}
+
+func newObjectID() string {
+	var b [12]byte
+	// Timestamp, 4 bytes, big endian
+	binary.BigEndian.PutUint32(b[:], uint32(time.Now().Unix()))
+	// Machine, first 3 bytes of md5(hostname)
+	b[4] = machineId[0]
+	b[5] = machineId[1]
+	b[6] = machineId[2]
+	// Pid, 2 bytes, specs don't specify endianness, but we use big endian.
+	b[7] = byte(processId >> 8)
+	b[8] = byte(processId)
+	// Increment, 3 bytes, big endian
+	i := atomic.AddUint32(&objectIdCounter, 1)
+	b[9] = byte(i >> 16)
+	b[10] = byte(i >> 8)
+	b[11] = byte(i)
+	return string(b[:])
+}
diff --git a/client/types.go b/client/types.go
index a998957..dd123b2 100644
--- a/client/types.go
+++ b/client/types.go
@@ -7,8 +7,6 @@ package client
 
 import (
 	"time"
-
-	"github.com/globalsign/mgo/bson"
 )
 
 // RequestData contains the info necessary for submitting a build to a remote service
@@ -21,17 +19,17 @@ type RequestData struct {
 
 // ResponseData contains the details of an individual build
 type ResponseData struct {
-	ID            bson.ObjectId `json:"id"`
-	CreatedBy     string        `json:"createdBy"`
-	SubmitTime    time.Time     `json:"submitTime"`
-	StartTime     *time.Time    `json:"startTime,omitempty" bson:",omitempty"`
-	IsComplete    bool          `json:"isComplete"`
-	CompleteTime  *time.Time    `json:"completeTime,omitempty"`
-	ImageSize     int64         `json:"imageSize,omitempty"`
-	ImageChecksum string        `json:"imageChecksum,omitempty"`
-	Definition    Definition    `json:"definition"`
-	WSURL         string        `json:"wsURL,omitempty" bson:"-"`
-	LibraryRef    string        `json:"libraryRef"`
-	LibraryURL    string        `json:"libraryURL"`
-	CallbackURL   string        `json:"callbackURL"`
+	ID            string     `json:"id"`
+	CreatedBy     string     `json:"createdBy"`
+	SubmitTime    time.Time  `json:"submitTime"`
+	StartTime     *time.Time `json:"startTime,omitempty"`
+	IsComplete    bool       `json:"isComplete"`
+	CompleteTime  *time.Time `json:"completeTime,omitempty"`
+	ImageSize     int64      `json:"imageSize,omitempty"`
+	ImageChecksum string     `json:"imageChecksum,omitempty"`
+	Definition    Definition `json:"definition"`
+	WSURL         string     `json:"wsURL,omitempty"`
+	LibraryRef    string     `json:"libraryRef"`
+	LibraryURL    string     `json:"libraryURL"`
+	CallbackURL   string     `json:"callbackURL"`
 }
diff --git a/go.mod b/go.mod
index 1299095..4f3c3a3 100644
--- a/go.mod
+++ b/go.mod
@@ -3,10 +3,7 @@ module github.com/sylabs/scs-build-client
 go 1.12
 
 require (
-	github.com/globalsign/mgo v0.0.0-20181015135952-eeefdecb41b8
 	github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b
 	github.com/gorilla/websocket v1.4.0
-	github.com/kr/pretty v0.1.0 // indirect
 	github.com/sylabs/json-resp v0.5.0
-	gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 // indirect
 )
diff --git a/go.sum b/go.sum
index 198a078..04ab81b 100644
--- a/go.sum
+++ b/go.sum
@@ -1,15 +1,6 @@
-github.com/globalsign/mgo v0.0.0-20181015135952-eeefdecb41b8 h1:DujepqpGd1hyOd7aW59XpK7Qymp8iy83xq74fLr21is=
-github.com/globalsign/mgo v0.0.0-20181015135952-eeefdecb41b8/go.mod h1:xkRDCp4j0OGD1HRkm4kmhM+pmpv3AKq5SU7GMg4oO/Q=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b h1:VKtxabqXZkF25pY9ekfRL6a582T4P37/31XEstQ5p58=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
 github.com/gorilla/websocket v1.4.0 h1:WDFjx/TMzVgy9VdMMQi2K2Emtwi2QcUQsztZ/zLaH/Q=
 github.com/gorilla/websocket v1.4.0/go.mod h1:E7qHFY5m1UJ88s3WnNqhKjPHQ0heANvMoAMk2YaljkQ=
-github.com/kr/pretty v0.1.0 h1:L/CwN0zerZDmRFUapSPitk6f+Q3+0za1rQkzVuMiMFI=
-github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
-github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
-github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
-github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
 github.com/sylabs/json-resp v0.5.0 h1:AWdKu6aS0WrkkltX1M0ex0lENrIcx5TISox902s2L2M=
 github.com/sylabs/json-resp v0.5.0/go.mod h1:anCzED2SGHHZQDubMuoVtwMuJZdpqQ+7iso8yDFm/nQ=
-gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 h1:qIbj1fsPNlZgppZ+VLlY7N33q108Sa+fhmuc+sWQYwY=
-gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=