diff --git a/homeassistant/package_constraints.txt b/homeassistant/package_constraints.txt
index f46248d2e1c..b88fef0f64f 100644
--- a/homeassistant/package_constraints.txt
+++ b/homeassistant/package_constraints.txt
@@ -25,6 +25,7 @@ bluetooth-data-tools==1.20.0
 cached-ipaddress==0.8.0
 certifi>=2021.5.30
 ciso8601==2.3.2
+cronsim==2.6
 cryptography==44.0.0
 dbus-fast==2.24.3
 fnv-hash-fast==1.0.2
diff --git a/pyproject.toml b/pyproject.toml
index 8c66e5a3bdd..3e432b6e8ad 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -42,6 +42,7 @@ dependencies    = [
     "bcrypt==4.2.0",
     "certifi>=2021.5.30",
     "ciso8601==2.3.2",
+    "cronsim==2.6",
     "fnv-hash-fast==1.0.2",
     # hass-nabucasa is imported by helpers which don't depend on the cloud
     # integration
diff --git a/requirements.txt b/requirements.txt
index 82405dc44ef..3f1fd48ed57 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -18,6 +18,7 @@ awesomeversion==24.6.0
 bcrypt==4.2.0
 certifi>=2021.5.30
 ciso8601==2.3.2
+cronsim==2.6
 fnv-hash-fast==1.0.2
 hass-nabucasa==0.87.0
 httpx==0.27.2