diff --git a/grpcv1.go b/grpcv1.go
index 1c891b94..b1e5c1ee 100644
--- a/grpcv1.go
+++ b/grpcv1.go
@@ -3,6 +3,7 @@ package headscale
 
 import (
 	"context"
+	"fmt"
 	"strings"
 	"time"
 
@@ -195,13 +196,11 @@ func (api headscaleV1APIServer) SetTags(
 	}
 
 	for _, tag := range request.GetTags() {
-		if strings.Index(tag, "tag:") != 0 {
+		err := validateTag(tag)
+		if err != nil {
 			return &v1.SetTagsResponse{
 					Machine: nil,
-				}, status.Error(
-					codes.InvalidArgument,
-					"Invalid tag detected. Each tag must start with the string 'tag:'",
-				)
+			}, status.Error(codes.InvalidArgument, err.Error())
 		}
 	}
 
@@ -220,6 +219,19 @@ func (api headscaleV1APIServer) SetTags(
 	return &v1.SetTagsResponse{Machine: machine.toProto()}, nil
 }
 
+func validateTag(tag string) error {
+	if strings.Index(tag, "tag:") != 0 {
+		return fmt.Errorf("tag must start with the string 'tag:'")
+	}
+	if strings.ToLower(tag) != tag {
+		return fmt.Errorf("tag should be lowercase")
+	}
+	if len(strings.Fields(tag)) > 1 {
+		return fmt.Errorf("tag should not contains space")
+	}
+	return nil
+}
+
 func (api headscaleV1APIServer) DeleteMachine(
 	ctx context.Context,
 	request *v1.DeleteMachineRequest,
diff --git a/grpcv1_test.go b/grpcv1_test.go
new file mode 100644
index 00000000..e48ae1ef
--- /dev/null
+++ b/grpcv1_test.go
@@ -0,0 +1,42 @@
+package headscale
+
+import "testing"
+
+func Test_validateTag(t *testing.T) {
+	type args struct {
+		tag string
+	}
+	tests := []struct {
+		name    string
+		args    args
+		wantErr bool
+	}{
+		{
+			name:    "valid tag",
+			args:    args{tag: "tag:test"},
+			wantErr: false,
+		},
+		{
+			name:    "tag without tag prefix",
+			args:    args{tag: "test"},
+			wantErr: true,
+		},
+		{
+			name:    "uppercase tag",
+			args:    args{tag: "tag:tEST"},
+			wantErr: true,
+		},
+		{
+			name:    "tag that contains space",
+			args:    args{tag: "tag:this is a spaced tag"},
+			wantErr: true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if err := validateTag(tt.args.tag); (err != nil) != tt.wantErr {
+				t.Errorf("validateTag() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}
diff --git a/integration_cli_test.go b/integration_cli_test.go
index f9ff5ec0..2f58e71d 100644
--- a/integration_cli_test.go
+++ b/integration_cli_test.go
@@ -625,7 +625,7 @@ func (s *IntegrationCLITestSuite) TestNodeTagCommand() {
 	var errorOutput errOutput
 	err = json.Unmarshal([]byte(wrongTagResult), &errorOutput)
 	assert.Nil(s.T(), err)
-	assert.Contains(s.T(), errorOutput.Error, "Invalid tag detected")
+	assert.Contains(s.T(), errorOutput.Error, "tag must start with the string 'tag:'")
 
 	// Test list all nodes after added seconds
 	listAllResult, err := ExecuteCommand(
diff --git a/machine.go b/machine.go
index 1bed2955..dda49020 100644
--- a/machine.go
+++ b/machine.go
@@ -374,7 +374,13 @@ func (h *Headscale) UpdateMachineFromDatabase(machine *Machine) error {
 
 // SetTags takes a Machine struct pointer and update the forced tags.
 func (h *Headscale) SetTags(machine *Machine, tags []string) error {
-	machine.ForcedTags = tags
+	newTags := []string{}
+	for _, tag := range tags {
+		if !contains(newTags, tag) {
+			newTags = append(newTags, tag)
+		}
+	}
+	machine.ForcedTags = newTags
 	if err := h.UpdateACLRules(); err != nil && !errors.Is(err, errEmptyPolicy) {
 		return err
 	}
diff --git a/machine_test.go b/machine_test.go
index a06d0db2..35c3eed9 100644
--- a/machine_test.go
+++ b/machine_test.go
@@ -280,6 +280,49 @@ func (s *Suite) TestSerdeAddressStrignSlice(c *check.C) {
 	}
 }
 
+func (s *Suite) TestSetTags(c *check.C) {
+	namespace, err := app.CreateNamespace("test")
+	c.Assert(err, check.IsNil)
+
+	pak, err := app.CreatePreAuthKey(namespace.Name, false, false, nil)
+	c.Assert(err, check.IsNil)
+
+	_, err = app.GetMachine("test", "testmachine")
+	c.Assert(err, check.NotNil)
+
+	machine := &Machine{
+		ID:             0,
+		MachineKey:     "foo",
+		NodeKey:        "bar",
+		DiscoKey:       "faa",
+		Hostname:       "testmachine",
+		NamespaceID:    namespace.ID,
+		RegisterMethod: RegisterMethodAuthKey,
+		AuthKeyID:      uint(pak.ID),
+	}
+	app.db.Save(machine)
+
+	// assign simple tags
+	sTags := []string{"tag:test", "tag:foo"}
+	err = app.SetTags(machine, sTags)
+	c.Assert(err, check.IsNil)
+	machine, err = app.GetMachine("test", "testmachine")
+	c.Assert(err, check.IsNil)
+	c.Assert(machine.ForcedTags, check.DeepEquals, StringList(sTags))
+
+	// assign duplicat tags, expect no errors but no doubles in DB
+	eTags := []string{"tag:bar", "tag:test", "tag:unknown", "tag:test"}
+	err = app.SetTags(machine, eTags)
+	c.Assert(err, check.IsNil)
+	machine, err = app.GetMachine("test", "testmachine")
+	c.Assert(err, check.IsNil)
+	c.Assert(
+		machine.ForcedTags,
+		check.DeepEquals,
+		StringList([]string{"tag:bar", "tag:test", "tag:unknown"}),
+	)
+}
+
 func Test_getTags(t *testing.T) {
 	type args struct {
 		aclPolicy        *ACLPolicy