diff --git a/mod/consensus-types/pkg/types/validator.go b/mod/consensus-types/pkg/types/validator.go
index 21c25287aa..a0e4640dc0 100644
--- a/mod/consensus-types/pkg/types/validator.go
+++ b/mod/consensus-types/pkg/types/validator.go
@@ -313,6 +313,10 @@ func (v *Validator) SetEffectiveBalance(balance math.Gwei) {
 	v.EffectiveBalance = balance
 }
 
+func (v *Validator) SetWithdrawableEpoch(e math.Epoch) {
+	v.WithdrawableEpoch = e
+}
+
 // GetWithdrawableEpoch returns the epoch when the validator can withdraw.
 func (v Validator) GetWithdrawableEpoch() math.Epoch {
 	return v.WithdrawableEpoch
diff --git a/mod/state-transition/pkg/core/state_processor_staking.go b/mod/state-transition/pkg/core/state_processor_staking.go
index a798b1fcfc..d784aa6edb 100644
--- a/mod/state-transition/pkg/core/state_processor_staking.go
+++ b/mod/state-transition/pkg/core/state_processor_staking.go
@@ -191,16 +191,38 @@ func (sp *StateProcessor[
 		math.Gwei(sp.cs.MaxEffectiveBalance()),
 	)
 
-	// TODO: This is a bug that lives on bArtio. Delete this eventually.
-	if sp.cs.DepositEth1ChainID() == bArtioChainID {
-		if err := st.AddValidatorBartio(val); err != nil {
+	// BeaconKit enforces a cap on the validator set size. If a deposit is made
+	// that would breach the cap, we mark the validator as immediately
+	// withdrawable, so that it will be evicted in the next block along with
+	// the amount deposited.
+	validators, err := st.GetValidators()
+	if err != nil {
+		return err
+	}
+
+	//#nosec:G701 // can't overflow.
+	if uint32(len(validators)) >= sp.cs.GetValidatorsSetCapSize() {
+		var slot math.Slot
+		slot, err = st.GetSlot()
+		if err != nil {
 			return err
 		}
-	} else if err := st.AddValidator(val); err != nil {
+
+		epoch := sp.cs.SlotToEpoch(slot)
+		val.SetWithdrawableEpoch(epoch)
+	}
+
+	// TODO: This is a bug that lives on bArtio. Delete this eventually.
+	if sp.cs.DepositEth1ChainID() == bArtioChainID {
+		return st.AddValidatorBartio(val)
+	}
+
+	if err = st.AddValidator(val); err != nil {
 		return err
 	}
 
-	idx, err := st.ValidatorIndexByPubkey(val.GetPubkey())
+	var idx math.U64
+	idx, err = st.ValidatorIndexByPubkey(val.GetPubkey())
 	if err != nil {
 		return err
 	}
diff --git a/mod/state-transition/pkg/core/types.go b/mod/state-transition/pkg/core/types.go
index 26ef877923..a3fc31e96f 100644
--- a/mod/state-transition/pkg/core/types.go
+++ b/mod/state-transition/pkg/core/types.go
@@ -232,6 +232,8 @@ type Validator[
 	SetEffectiveBalance(math.Gwei)
 	// GetWithdrawableEpoch returns the epoch when the validator can withdraw.
 	GetWithdrawableEpoch() math.Epoch
+
+	SetWithdrawableEpoch(math.Epoch)
 }
 
 type Validators interface {