diff --git a/chain/stmgr/stmgr.go b/chain/stmgr/stmgr.go
index c872048b0..5a6434c4e 100644
--- a/chain/stmgr/stmgr.go
+++ b/chain/stmgr/stmgr.go
@@ -8,6 +8,7 @@ import (
 	"github.com/filecoin-project/go-address"
 	amt "github.com/filecoin-project/go-amt-ipld/v2"
 	"github.com/filecoin-project/lotus/api"
+	"github.com/filecoin-project/lotus/build"
 	"github.com/filecoin-project/lotus/chain/actors"
 	"github.com/filecoin-project/lotus/chain/state"
 	"github.com/filecoin-project/lotus/chain/store"
@@ -236,7 +237,7 @@ func (sm *StateManager) ApplyBlocks(ctx context.Context, pstate cid.Cid, bms []B
 		Nonce:    ca.Nonce,
 		Value:    types.NewInt(0),
 		GasPrice: types.NewInt(0),
-		GasLimit: 1 << 30, // Make super sure this is never too little
+		GasLimit: build.BlockGasLimit * 10, // Make super sure this is never too little
 		Method:   builtin.MethodsCron.EpochTick,
 		Params:   nil,
 	}
diff --git a/chain/vm/runtime.go b/chain/vm/runtime.go
index 9e64275e3..039bccc0b 100644
--- a/chain/vm/runtime.go
+++ b/chain/vm/runtime.go
@@ -550,7 +550,8 @@ func (rt *Runtime) chargeGasInternal(gas GasCharge, skip int) aerrors.ActorError
 	rt.lastGasChargeTime = now
 	rt.lastGasCharge = &gasTrace
 
-	if rt.gasUsed+toUse > rt.gasAvailable {
+	// overflow safe
+	if rt.gasUsed > rt.gasAvailable-toUse {
 		rt.gasUsed = rt.gasAvailable
 		return aerrors.Newf(exitcode.SysErrOutOfGas, "not enough gas: used=%d, available=%d",
 			rt.gasUsed, rt.gasAvailable)