diff --git a/pkcs11/src/config/initialization.rs b/pkcs11/src/config/initialization.rs
index b156b824..a10b6d3d 100644
--- a/pkcs11/src/config/initialization.rs
+++ b/pkcs11/src/config/initialization.rs
@@ -27,6 +27,8 @@ pub enum InitializationError {
     NoCerts,
     #[error("No operator or administrator for slot: {0}")]
     NoUser(String),
+    #[error("No instance given for a slot")]
+    NoInstance,
 }
 
 pub fn initialize_with_configs(
@@ -288,7 +290,11 @@ fn slot_from_config(slot: &SlotConfig) -> Result<Slot, InitializationError> {
             };
             Ok(api_config)
         })
-        .collect::<Result<_, InitializationError>>()?;
+        .collect::<Result<Arc<_>, InitializationError>>()?;
+    if instances.is_empty() {
+        error!("Slot without any instance configured");
+        return Err(InitializationError::NoInstance);
+    }
 
     Ok(Slot {
         _description: slot.description.clone(),