diff --git a/server/channels/app/bot.go b/server/channels/app/bot.go
index 1f95f04b7e..302e7951f3 100644
--- a/server/channels/app/bot.go
+++ b/server/channels/app/bot.go
@@ -65,18 +65,19 @@ func (a *App) EnsureBot(rctx request.CTX, pluginID string, bot *model.Bot) (stri
 			if appErr := a.SetPluginKey(pluginID, botUserKey, []byte(user.Id)); appErr != nil {
 				return "", fmt.Errorf("failed to set plugin key: %w", appErr)
 			}
-		} else {
-			rctx.Logger().Error("Plugin attempted to use an account that already exists. Convert user to a bot "+
-				"account in the CLI by running 'mattermost user convert <username> --bot'. If the user is an "+
-				"existing user account you want to preserve, change its username and restart the Mattermost server, "+
-				"after which the plugin will create a bot account with that name. For more information about bot "+
-				"accounts, see https://mattermost.com/pl/default-bot-accounts", mlog.String("username",
-				bot.Username),
-				mlog.String("user_id",
-					user.Id),
-			)
+			return user.Id, nil
 		}
-		return user.Id, nil
+
+		rctx.Logger().Error("Plugin attempted to use an account that already exists. Convert user to a bot "+
+			"account in the CLI by running 'mattermost user convert <username> --bot'. If the user is an "+
+			"existing user account you want to preserve, change its username and restart the Mattermost server, "+
+			"after which the plugin will create a bot account with that name. For more information about bot "+
+			"accounts, see https://mattermost.com/pl/default-bot-accounts", mlog.String("username",
+			bot.Username),
+			mlog.String("user_id",
+				user.Id),
+		)
+		return "", fmt.Errorf("username %q is already taken by a non-bot user", bot.Username)
 	}
 
 	createdBot, err := a.CreateBot(rctx, bot)
diff --git a/server/channels/app/bot_test.go b/server/channels/app/bot_test.go
index 9dd4cf8156..aa68a4dedf 100644
--- a/server/channels/app/bot_test.go
+++ b/server/channels/app/bot_test.go
@@ -152,6 +152,23 @@ func TestEnsureBot(t *testing.T) {
 		assert.Equal(t, "another bot", bot.Description)
 	})
 
+	t.Run("ensure bot should fail if username belongs to a non-bot user", func(t *testing.T) {
+		th := Setup(t).InitBasic()
+		defer th.TearDown()
+
+		pluginId := "pluginId"
+
+		// th.BasicUser is a regular (non-bot) user created by InitBasic.
+		// EnsureBot must return an error — not the human user's ID.
+		botID, err := th.App.EnsureBot(th.Context, pluginId, &model.Bot{
+			Username:    th.BasicUser.Username,
+			Description: "a bot",
+			OwnerId:     th.BasicUser.Id,
+		})
+		require.Error(t, err)
+		assert.Empty(t, botID)
+	})
+
 	t.Run("ensure bot should pass even after delete bot user", func(t *testing.T) {
 		th := Setup(t).InitBasic()
 		defer th.TearDown()