diff --git a/beacon_node/beacon_chain/src/beacon_chain.rs b/beacon_node/beacon_chain/src/beacon_chain.rs
index f6cef7dac..afc7a992a 100644
--- a/beacon_node/beacon_chain/src/beacon_chain.rs
+++ b/beacon_node/beacon_chain/src/beacon_chain.rs
@@ -466,6 +466,14 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
             state.build_committee_cache(RelativeEpoch::Current, &self.spec)?;
         }
 
+        if epoch(state.as_ref().slot) != epoch(slot) {
+            return Err(Error::InvariantViolated(format!(
+                "Epochs in consistent in proposer lookup: state: {}, requested: {}",
+                epoch(state.as_ref().slot),
+                epoch(slot)
+            )));
+        }
+
         state
             .as_ref()
             .get_beacon_proposer_index(slot, RelativeEpoch::Current, &self.spec)
@@ -494,6 +502,14 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
             state.build_committee_cache(RelativeEpoch::Current, &self.spec)?;
         }
 
+        if as_epoch(state.as_ref().slot) != epoch {
+            return Err(Error::InvariantViolated(format!(
+                "Epochs in consistent in attestation duties lookup: state: {}, requested: {}",
+                as_epoch(state.as_ref().slot),
+                epoch
+            )));
+        }
+
         if let Some(attestation_duty) = state
             .as_ref()
             .get_attestation_duties(validator_index, RelativeEpoch::Current)?
@@ -1123,13 +1139,9 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         slot: Slot,
     ) -> Result<(BeaconBlock<T::EthSpec>, BeaconState<T::EthSpec>), BlockProductionError> {
         let state = self
-            .state_at_slot(slot)
+            .state_at_slot(slot - 1)
             .map_err(|_| BlockProductionError::UnableToProduceAtSlot(slot))?;
 
-        let slot = self
-            .slot()
-            .map_err(|_| BlockProductionError::UnableToReadSlot)?;
-
         self.produce_block_on_state(state.as_ref().clone(), slot, randao_reveal)
     }
 
diff --git a/beacon_node/beacon_chain/src/errors.rs b/beacon_node/beacon_chain/src/errors.rs
index cd8d6aad6..5ef68f2cd 100644
--- a/beacon_node/beacon_chain/src/errors.rs
+++ b/beacon_node/beacon_chain/src/errors.rs
@@ -37,6 +37,8 @@ pub enum BeaconChainError {
         beacon_block_root: Hash256,
     },
     AttestationValidationError(AttestationValidationError),
+    /// Returned when an internal check fails, indicating corrupt data.
+    InvariantViolated(String),
 }
 
 easy_from_to!(SlotProcessingError, BeaconChainError);
diff --git a/beacon_node/rpc/src/beacon_block.rs b/beacon_node/rpc/src/beacon_block.rs
index f6be6207f..346d7e263 100644
--- a/beacon_node/rpc/src/beacon_block.rs
+++ b/beacon_node/rpc/src/beacon_block.rs
@@ -34,8 +34,7 @@ impl<T: BeaconChainTypes> BeaconBlockService for BeaconBlockServiceInstance<T> {
         trace!(self.log, "Generating a beacon block"; "req" => format!("{:?}", req));
 
         // decode the request
-        // TODO: requested slot currently unused, see: https://github.com/sigp/lighthouse/issues/336
-        let _requested_slot = Slot::from(req.get_slot());
+        let requested_slot = Slot::from(req.get_slot());
         let randao_reveal = match Signature::from_ssz_bytes(req.get_randao_reveal()) {
             Ok(reveal) => reveal,
             Err(_) => {
@@ -51,22 +50,7 @@ impl<T: BeaconChainTypes> BeaconBlockService for BeaconBlockServiceInstance<T> {
             }
         };
 
-        let slot = match self.chain.slot() {
-            Ok(slot) => slot,
-            Err(_) => {
-                // decode error, incorrect signature
-                let log_clone = self.log.clone();
-                let f = sink
-                    .fail(RpcStatus::new(
-                        RpcStatusCode::InvalidArgument,
-                        Some("No slot from chain".to_string()),
-                    ))
-                    .map_err(move |e| warn!(log_clone, "failed to reply {:?}: {:?}", req, e));
-                return ctx.spawn(f);
-            }
-        };
-
-        let produced_block = match self.chain.produce_block(randao_reveal, slot) {
+        let produced_block = match self.chain.produce_block(randao_reveal, requested_slot) {
             Ok((block, _state)) => block,
             Err(e) => {
                 // could not produce a block
@@ -82,6 +66,11 @@ impl<T: BeaconChainTypes> BeaconBlockService for BeaconBlockServiceInstance<T> {
             }
         };
 
+        assert_eq!(
+            produced_block.slot, requested_slot,
+            "should produce at the requested slot"
+        );
+
         let mut block = BeaconBlockProto::new();
         block.set_ssz(ssz_encode(&produced_block));
 
diff --git a/beacon_node/rpc/src/validator.rs b/beacon_node/rpc/src/validator.rs
index 2a1ad45f4..84995ca50 100644
--- a/beacon_node/rpc/src/validator.rs
+++ b/beacon_node/rpc/src/validator.rs
@@ -46,12 +46,20 @@ impl<T: BeaconChainTypes> ValidatorService for ValidatorServiceInstance<T> {
 
         let _ = state.build_all_caches(&self.chain.spec);
 
+        assert_eq!(
+            state.current_epoch(),
+            epoch,
+            "Retrieved state should be from the same epoch"
+        );
+
         let mut resp = GetDutiesResponse::new();
         let resp_validators = resp.mut_active_validators();
 
         let validator_proposers: Result<Vec<usize>, _> = epoch
             .slot_iter(T::EthSpec::slots_per_epoch())
-            .map(|slot| self.chain.block_proposer(slot))
+            .map(|slot| {
+                state.get_beacon_proposer_index(slot, RelativeEpoch::Current, &self.chain.spec)
+            })
             .collect();
         let validator_proposers = match validator_proposers {
             Ok(v) => v,