diff --git a/src/py/flwr/cli/build.py b/src/py/flwr/cli/build.py
index 4c9dca4ebcf1..e86f4bb762b3 100644
--- a/src/py/flwr/cli/build.py
+++ b/src/py/flwr/cli/build.py
@@ -81,8 +81,8 @@ def build(
     if not is_valid_project_name(app.name):
         typer.secho(
             f"❌ The project name {app.name} is invalid, "
-            "a valid project name must start with a letter or an underscore, "
-            "and can only contain letters, digits, and underscores.",
+            "a valid project name must start with a letter, "
+            "and can only contain letters, digits, and hyphens.",
             fg=typer.colors.RED,
             bold=True,
         )