diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index b0b4fdce5..7f9d3964a 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -1482,7 +1482,9 @@ def process_slashings(state: BeaconState) -> None:
     total_balance = get_total_active_balance(state)
     for index, validator in enumerate(state.validators):
         if validator.slashed and epoch + EPOCHS_PER_SLASHINGS_VECTOR // 2 == validator.withdrawable_epoch:
-            penalty = validator.effective_balance * min(sum(state.slashings) * 3, total_balance) // total_balance
+            increment = EFFECTIVE_BALANCE_INCREMENT  # Factored out from penalty numerator to avoid uint64 overflow
+            penalty_numerator = validator.effective_balance // increment * min(sum(state.slashings) * 3, total_balance)
+            penalty = penalty_numerator // total_balance * increment
             decrease_balance(state, ValidatorIndex(index), penalty)
 ```
 
diff --git a/test_libs/pyspec/eth2spec/test/phase_0/epoch_processing/test_process_slashings.py b/test_libs/pyspec/eth2spec/test/phase_0/epoch_processing/test_process_slashings.py
index 7be23a04d..c58da5a4a 100644
--- a/test_libs/pyspec/eth2spec/test/phase_0/epoch_processing/test_process_slashings.py
+++ b/test_libs/pyspec/eth2spec/test/phase_0/epoch_processing/test_process_slashings.py
@@ -66,8 +66,13 @@ def test_small_penalty(spec, state):
     spec.process_slashings(state)
     yield 'post', state
 
-    assert state.balances[0] == pre_slash_balances[0] - (state.validators[0].effective_balance
-                                                         * 3 * total_penalties // total_balance)
+    expected_penalty = (
+        state.validators[0].effective_balance // spec.EFFECTIVE_BALANCE_INCREMENT
+        * (3 * total_penalties)
+        // total_balance
+        * spec.EFFECTIVE_BALANCE_INCREMENT
+    )
+    assert state.balances[0] == pre_slash_balances[0] - expected_penalty
 
 
 @with_all_phases
@@ -121,5 +126,10 @@ def test_scaled_penalties(spec, state):
 
     for i in slashed_indices:
         v = state.validators[i]
-        penalty = v.effective_balance * total_penalties * 3 // total_balance
-        assert state.balances[i] == pre_slash_balances[i] - penalty
+        expected_penalty = (
+            v.effective_balance // spec.EFFECTIVE_BALANCE_INCREMENT
+            * (3 * total_penalties)
+            // (total_balance)
+            * spec.EFFECTIVE_BALANCE_INCREMENT
+        )
+        assert state.balances[i] == pre_slash_balances[i] - expected_penalty