diff --git a/poetry.lock b/poetry.lock
index 3bb5c45..f41250d 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -403,4 +403,4 @@ test = ["covdefaults (>=2.3)", "coverage (>=7.2.7)", "coverage-enable-subprocess
 [metadata]
 lock-version = "2.0"
 python-versions = "^3.13"
-content-hash = "7f853bdda7a4b19de579a9c54d756d25b9d75a79736c3f1439b0d37d41ac25ac"
+content-hash = "1c2812806ab8c56e09acb3105aa4f94bcca569ed25fc4ded38865e5c9b8afaab"
diff --git a/pyproject.toml b/pyproject.toml
index 644ced0..27236d7 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -15,7 +15,7 @@ python = "^3.13"
 [tool.poetry.scripts]
 mirro = "mirro.main:main"
 
-[tool.poetry.group.dev.dependencies]
+[tool.poetry.dev-dependencies]
 pytest = "^9.0.1"
 pytest-cov = "^7.0.0"
 pre-commit = "^3.8"
diff --git a/src/mirro/main.py b/src/mirro/main.py
index fa0102d..7d7fe54 100644
--- a/src/mirro/main.py
+++ b/src/mirro/main.py
@@ -31,7 +31,7 @@ def backup_original(
     timestamp = time.strftime("%Y-%m-%d %H:%M:%S UTC", time.gmtime())
     shortstamp = time.strftime("%Y%m%dT%H%M%S", time.gmtime())
 
-    backup_name = f"{original_path.name}.orig.{shortstamp}.bak"
+    backup_name = f"{original_path.name}.orig.{shortstamp}"
     backup_path = backup_dir / backup_name
 
     header = (