diff --git a/contracts/staking/contracts/src/fees/MixinExchangeFees.sol b/contracts/staking/contracts/src/fees/MixinExchangeFees.sol
index 239145da75..5208d1d0ba 100644
--- a/contracts/staking/contracts/src/fees/MixinExchangeFees.sol
+++ b/contracts/staking/contracts/src/fees/MixinExchangeFees.sol
@@ -97,7 +97,7 @@ contract MixinExchangeFees is
             totalWeightedStakeThisEpoch = totalWeightedStakeThisEpoch.safeAdd(pool.weightedStake);
 
             // Increase the number of active pools.
-            numActivePoolsThisEpoch += 1;
+            numActivePoolsThisEpoch = numActivePoolsThisEpoch.safeAdd(1);
 
             // Emit an event so keepers know what pools to pass into
             // `finalize()`.
diff --git a/contracts/staking/contracts/src/staking_pools/MixinStakingPoolRewards.sol b/contracts/staking/contracts/src/staking_pools/MixinStakingPoolRewards.sol
index bf0af0b4b8..098273f80e 100644
--- a/contracts/staking/contracts/src/staking_pools/MixinStakingPoolRewards.sol
+++ b/contracts/staking/contracts/src/staking_pools/MixinStakingPoolRewards.sol
@@ -211,7 +211,7 @@ contract MixinStakingPoolRewards is
                 PPM_DENOMINATOR,
                 totalReward
             );
-            membersReward = totalReward - operatorReward;
+            membersReward = totalReward.safeSub(operatorReward);
         }
         return (operatorReward, membersReward);
     }
diff --git a/contracts/staking/contracts/src/sys/MixinFinalizer.sol b/contracts/staking/contracts/src/sys/MixinFinalizer.sol
index f6808d72bf..048eba11e6 100644
--- a/contracts/staking/contracts/src/sys/MixinFinalizer.sol
+++ b/contracts/staking/contracts/src/sys/MixinFinalizer.sol
@@ -50,7 +50,7 @@ contract MixinFinalizer is
         if (state.poolsRemaining != 0) {
             LibRichErrors.rrevert(
                 LibStakingRichErrors.PreviousEpochNotFinalizedError(
-                    closingEpoch - 1,
+                    closingEpoch.safeSub(1),
                     state.poolsRemaining
                 )
             );