diff --git a/http/handler/api/restream.go b/http/handler/api/restream.go
index a72fb4c8..be5741b8 100644
--- a/http/handler/api/restream.go
+++ b/http/handler/api/restream.go
@@ -187,7 +187,11 @@ func (h *RestreamHandler) Update(c echo.Context) error {
 	config := process.Marshal()
 
 	if err := h.restream.UpdateProcess(id, config); err != nil {
-		return api.Err(http.StatusBadRequest, "Process can't be updated", "%s", err)
+		if err == restream.ErrUnknownProcess {
+			return api.Err(http.StatusNotFound, "Process not found: %s", id)
+		}
+
+		return api.Err(http.StatusBadRequest, "Process can't be updated: %s", err)
 	}
 
 	p, _ := h.getProcess(config.ID, "config")
diff --git a/http/handler/api/restream_test.go b/http/handler/api/restream_test.go
index 713a4f10..516db9ce 100644
--- a/http/handler/api/restream_test.go
+++ b/http/handler/api/restream_test.go
@@ -110,7 +110,39 @@ func TestUpdateProcessInvalid(t *testing.T) {
 	mock.Request(t, http.StatusOK, router, "GET", "/"+proc.ID, nil)
 }
 
-func TestUpdateProcess(t *testing.T) {
+func TestUpdateReplaceProcess(t *testing.T) {
+	router, err := getDummyRestreamRouter()
+	require.NoError(t, err)
+
+	data := mock.Read(t, "./fixtures/addProcess.json")
+
+	response := mock.Request(t, http.StatusOK, router, "POST", "/", data)
+
+	mock.Validate(t, &api.ProcessConfig{}, response.Data)
+
+	update := bytes.Buffer{}
+	_, err = update.ReadFrom(mock.Read(t, "./fixtures/addProcess.json"))
+	require.NoError(t, err)
+
+	proc := api.ProcessConfig{}
+	err = json.Unmarshal(update.Bytes(), &proc)
+	require.NoError(t, err)
+
+	encoded, err := json.Marshal(&proc)
+	require.NoError(t, err)
+
+	update.Reset()
+	_, err = update.Write(encoded)
+	require.NoError(t, err)
+
+	response = mock.Request(t, http.StatusOK, router, "PUT", "/test", &update)
+
+	mock.Validate(t, &api.ProcessConfig{}, response.Data)
+
+	mock.Request(t, http.StatusOK, router, "GET", "/test", nil)
+}
+
+func TestUpdateNewProcess(t *testing.T) {
 	router, err := getDummyRestreamRouter()
 	require.NoError(t, err)
 
@@ -128,7 +160,6 @@ func TestUpdateProcess(t *testing.T) {
 	err = json.Unmarshal(update.Bytes(), &proc)
 	require.NoError(t, err)
 
-	// invalid address
 	proc.ID = "test2"
 
 	encoded, err := json.Marshal(&proc)
@@ -146,6 +177,15 @@ func TestUpdateProcess(t *testing.T) {
 	mock.Request(t, http.StatusOK, router, "GET", "/test2", nil)
 }
 
+func TestUpdateNonExistentProcess(t *testing.T) {
+	router, err := getDummyRestreamRouter()
+	require.NoError(t, err)
+
+	data := mock.Read(t, "./fixtures/addProcess.json")
+
+	mock.Request(t, http.StatusNotFound, router, "PUT", "/test", data)
+}
+
 func TestRemoveUnknownProcess(t *testing.T) {
 	router, err := getDummyRestreamRouter()
 	require.NoError(t, err)
diff --git a/restream/restream.go b/restream/restream.go
index c58b235e..0c6be4aa 100644
--- a/restream/restream.go
+++ b/restream/restream.go
@@ -2,6 +2,7 @@ package restream
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"path/filepath"
 	"regexp"
@@ -352,6 +353,9 @@ func (r *restream) CreatedAt() time.Time {
 	return r.createdAt
 }
 
+var ErrUnknownProcess = errors.New("unknown process")
+var ErrProcessExists = errors.New("process already exists")
+
 func (r *restream) AddProcess(config *app.Config) error {
 	r.lock.RLock()
 	t, err := r.createTask(config)
@@ -366,7 +370,7 @@ func (r *restream) AddProcess(config *app.Config) error {
 
 	_, ok := r.tasks[t.id]
 	if ok {
-		return fmt.Errorf("the process ID '%s' already exists", t.id)
+		return ErrProcessExists
 	}
 
 	r.tasks[t.id] = t
@@ -841,7 +845,7 @@ func (r *restream) UpdateProcess(id string, config *app.Config) error {
 
 	task, ok := r.tasks[id]
 	if !ok {
-		return fmt.Errorf("unknown process ID (%s)", id)
+		return ErrUnknownProcess
 	}
 
 	t.process.Order = task.process.Order
@@ -849,7 +853,7 @@ func (r *restream) UpdateProcess(id string, config *app.Config) error {
 	if id != t.id {
 		_, ok := r.tasks[t.id]
 		if ok {
-			return fmt.Errorf("the process ID '%s' already exists", t.id)
+			return ErrProcessExists
 		}
 	}
 
@@ -896,7 +900,7 @@ func (r *restream) GetProcess(id string) (*app.Process, error) {
 
 	task, ok := r.tasks[id]
 	if !ok {
-		return &app.Process{}, fmt.Errorf("unknown process ID (%s)", id)
+		return &app.Process{}, ErrUnknownProcess
 	}
 
 	process := task.process.Clone()
@@ -921,7 +925,7 @@ func (r *restream) DeleteProcess(id string) error {
 func (r *restream) deleteProcess(id string) error {
 	task, ok := r.tasks[id]
 	if !ok {
-		return fmt.Errorf("unknown process ID (%s)", id)
+		return ErrUnknownProcess
 	}
 
 	if task.process.Order != "stop" {
@@ -954,7 +958,7 @@ func (r *restream) StartProcess(id string) error {
 func (r *restream) startProcess(id string) error {
 	task, ok := r.tasks[id]
 	if !ok {
-		return fmt.Errorf("unknown process ID (%s)", id)
+		return ErrUnknownProcess
 	}
 
 	if !task.valid {
@@ -997,7 +1001,7 @@ func (r *restream) StopProcess(id string) error {
 func (r *restream) stopProcess(id string) error {
 	task, ok := r.tasks[id]
 	if !ok {
-		return fmt.Errorf("unknown process ID (%s)", id)
+		return ErrUnknownProcess
 	}
 
 	status := task.ffmpeg.Status()
@@ -1025,7 +1029,7 @@ func (r *restream) RestartProcess(id string) error {
 func (r *restream) restartProcess(id string) error {
 	task, ok := r.tasks[id]
 	if !ok {
-		return fmt.Errorf("unknown process ID (%s)", id)
+		return ErrUnknownProcess
 	}
 
 	if !task.valid {
@@ -1058,7 +1062,7 @@ func (r *restream) ReloadProcess(id string) error {
 func (r *restream) reloadProcess(id string) error {
 	t, ok := r.tasks[id]
 	if !ok {
-		return fmt.Errorf("unknown process ID (%s)", id)
+		return ErrUnknownProcess
 	}
 
 	t.valid = false
@@ -1122,7 +1126,7 @@ func (r *restream) GetProcessState(id string) (*app.State, error) {
 
 	task, ok := r.tasks[id]
 	if !ok {
-		return state, fmt.Errorf("unknown process ID (%s)", id)
+		return state, ErrUnknownProcess
 	}
 
 	if !task.valid {
@@ -1183,7 +1187,7 @@ func (r *restream) GetProcessLog(id string) (*app.Log, error) {
 
 	task, ok := r.tasks[id]
 	if !ok {
-		return &app.Log{}, fmt.Errorf("unknown process ID (%s)", id)
+		return &app.Log{}, ErrUnknownProcess
 	}
 
 	if !task.valid {
@@ -1301,7 +1305,7 @@ func (r *restream) GetPlayout(id, inputid string) (string, error) {
 
 	task, ok := r.tasks[id]
 	if !ok {
-		return "", fmt.Errorf("unknown process ID '%s'", id)
+		return "", ErrUnknownProcess
 	}
 
 	if !task.valid {
@@ -1326,7 +1330,7 @@ func (r *restream) SetProcessMetadata(id, key string, data interface{}) error {
 
 	task, ok := r.tasks[id]
 	if !ok {
-		return fmt.Errorf("unknown process ID (%s)", id)
+		return ErrUnknownProcess
 	}
 
 	if task.metadata == nil {
@@ -1354,7 +1358,7 @@ func (r *restream) GetProcessMetadata(id, key string) (interface{}, error) {
 
 	task, ok := r.tasks[id]
 	if !ok {
-		return nil, fmt.Errorf("unknown process ID '%s'", id)
+		return nil, ErrUnknownProcess
 	}
 
 	if len(key) == 0 {