diff --git a/models/error.go b/models/error.go
index b6fe3128d35..42cbc6bb16a 100644
--- a/models/error.go
+++ b/models/error.go
@@ -434,3 +434,19 @@ func IsErrInvalidTeamRight(err error) bool {
 func (err ErrInvalidTeamRight) Error() string {
 	return fmt.Sprintf("The right is invalid [Right: %d]", err.Right)
 }
+
+// ErrTeamAlreadyHasAccess represents an error where a team already has access to a list/namespace
+type ErrTeamAlreadyHasAccess struct {
+	TeamID int64
+	ID int64
+}
+
+// IsErrTeamAlreadyHasAccess checks if an error is ErrTeamAlreadyHasAccess.
+func IsErrTeamAlreadyHasAccess(err error) bool {
+	_, ok := err.(ErrTeamAlreadyHasAccess)
+	return ok
+}
+
+func (err ErrTeamAlreadyHasAccess) Error() string {
+	return fmt.Sprintf("This team already has access. [Team ID: %d, ID: %d]", err.TeamID, err.ID)
+}
\ No newline at end of file
diff --git a/models/team_list_create.go b/models/team_list_create.go
index 3ed547f0322..830f0c63aac 100644
--- a/models/team_list_create.go
+++ b/models/team_list_create.go
@@ -20,6 +20,17 @@ func (tl *TeamList) Create(doer *User) (err error) {
 		return
 	}
 
+	// Check if the team is already on the list
+	exists, err := x.Where("team_id = ?", tl.TeamID).
+		And("list_id = ?", tl.ListID).
+		Get(&TeamList{})
+	if err != nil {
+		return
+	}
+	if exists {
+		return ErrTeamAlreadyHasAccess{tl.TeamID, tl.ListID}
+	}
+
 	// Insert the new team
 	_, err = x.Insert(tl)
 	return
diff --git a/models/team_members_create.go b/models/team_members_create.go
index 25fc01d323d..dfb555849c2 100644
--- a/models/team_members_create.go
+++ b/models/team_members_create.go
@@ -2,7 +2,7 @@ package models
 
 // Create implements the create method to assign a user to a team
 func (tm *TeamMember) Create(doer *User) (err error) {
-	//tm.TeamID = id
+	// TODO: Check if it exists etc
 	_, err = x.Insert(tm)
 	return
 }
diff --git a/models/team_namespace_create.go b/models/team_namespace_create.go
index 3a365990de1..f8f307126b5 100644
--- a/models/team_namespace_create.go
+++ b/models/team_namespace_create.go
@@ -19,6 +19,17 @@ func (tn *TeamNamespace) Create(doer *User) (err error) {
 	if err != nil {
 		return
 	}
+	
+	// Check if the team already has access to the namespace
+	exists, err := x.Where("team_id = ?", tn.TeamID).
+		And("namespace_id = ?", tn.NamespaceID).
+		Get(&TeamNamespace{})
+	if err != nil {
+		return
+	}
+	if exists {
+		return ErrTeamAlreadyHasAccess{tn.TeamID, tn.NamespaceID}
+	}
 
 	// Insert the new team
 	_, err = x.Insert(tn)
diff --git a/routes/crud/create.go b/routes/crud/create.go
index 5fea52a28f1..fb95dbcbbb7 100644
--- a/routes/crud/create.go
+++ b/routes/crud/create.go
@@ -53,6 +53,10 @@ func (c *WebHandler) CreateWeb(ctx echo.Context) error {
 			return echo.NewHTTPError(http.StatusBadRequest, "The team name cannot be empty.")
 		}
 
+		if models.IsErrTeamAlreadyHasAccess(err) {
+			return echo.NewHTTPError(http.StatusBadRequest, "This team already has access.")
+		}
+
 		return echo.NewHTTPError(http.StatusInternalServerError)
 	}