diff --git a/beacon-chain/core/blocks/BUILD.bazel b/beacon-chain/core/blocks/BUILD.bazel
index d564be7f1074..7ba2bc10bda5 100644
--- a/beacon-chain/core/blocks/BUILD.bazel
+++ b/beacon-chain/core/blocks/BUILD.bazel
@@ -60,6 +60,7 @@ go_test(
         "exit_test.go",
         "genesis_test.go",
         "header_test.go",
+        "proposer_slashing_regression_test.go",
         "proposer_slashing_test.go",
         "randao_test.go",
     ],
diff --git a/beacon-chain/core/blocks/proposer_slashing.go b/beacon-chain/core/blocks/proposer_slashing.go
index 4af10206b5eb..84caf8c3a325 100644
--- a/beacon-chain/core/blocks/proposer_slashing.go
+++ b/beacon-chain/core/blocks/proposer_slashing.go
@@ -4,13 +4,14 @@ import (
 	"context"
 	"fmt"
 
+	"github.com/prysmaticlabs/prysm/shared/params"
+
 	"github.com/gogo/protobuf/proto"
 	"github.com/pkg/errors"
 	ethpb "github.com/prysmaticlabs/ethereumapis/eth/v1alpha1"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
 	v "github.com/prysmaticlabs/prysm/beacon-chain/core/validators"
 	stateTrie "github.com/prysmaticlabs/prysm/beacon-chain/state"
-	"github.com/prysmaticlabs/prysm/shared/params"
 )
 
 // ProcessProposerSlashings is one of the operations performed
@@ -86,7 +87,7 @@ func VerifyProposerSlashing(
 	if err != nil {
 		return err
 	}
-	if !helpers.IsSlashableValidatorUsingTrie(proposer, helpers.SlotToEpoch(hSlot)) {
+	if !helpers.IsSlashableValidatorUsingTrie(proposer, helpers.CurrentEpoch(beaconState)) {
 		return fmt.Errorf("validator with key %#x is not slashable", proposer.PublicKey())
 	}
 	headers := []*ethpb.SignedBeaconBlockHeader{slashing.Header_1, slashing.Header_2}
@@ -96,6 +97,5 @@ func VerifyProposerSlashing(
 			return errors.Wrap(err, "could not verify beacon block header")
 		}
 	}
-
 	return nil
 }
diff --git a/beacon-chain/core/blocks/proposer_slashing_regression_test.go b/beacon-chain/core/blocks/proposer_slashing_regression_test.go
new file mode 100644
index 000000000000..64a59382b495
--- /dev/null
+++ b/beacon-chain/core/blocks/proposer_slashing_regression_test.go
@@ -0,0 +1,38 @@
+package blocks_test
+
+import (
+	"io/ioutil"
+	"testing"
+
+	"github.com/prysmaticlabs/prysm/beacon-chain/core/blocks"
+
+	ethpb "github.com/prysmaticlabs/ethereumapis/eth/v1alpha1"
+	stateTrie "github.com/prysmaticlabs/prysm/beacon-chain/state"
+	pb "github.com/prysmaticlabs/prysm/proto/beacon/p2p/v1"
+	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+)
+
+// Beaconfuzz discovered an issue where a proposer slashing could be produced which would pass
+// validation where we use the slashing's slot instead of the current epoch of our state for validation.
+// This would lead to us accepting an invalid slashing by marking the respective validator as 'slashable'
+// when it was not in actuality.
+// See: https://github.com/sigp/beacon-fuzz/issues/91
+func TestVerifyProposerSlashing_BeaconFuzzIssue91(t *testing.T) {
+	file, err := ioutil.ReadFile("testdata/beaconfuzz_91_beacon.ssz")
+	require.NoError(t, err)
+	rawState := &pb.BeaconState{}
+	err = rawState.UnmarshalSSZ(file)
+	require.NoError(t, err)
+
+	st, err := stateTrie.InitializeFromProtoUnsafe(rawState)
+	require.NoError(t, err)
+
+	file, err = ioutil.ReadFile("testdata/beaconfuzz_91_proposer_slashing.ssz")
+	require.NoError(t, err)
+	slashing := &ethpb.ProposerSlashing{}
+	err = slashing.UnmarshalSSZ(file)
+	require.NoError(t, err)
+
+	err = blocks.VerifyProposerSlashing(st, slashing)
+	require.ErrorContains(t, "validator with key 0x97f1d3a73197d7942695638c4fa9ac0fc3688c4f9774b905a14e3a3f171bac586c55e83ff97a1aeffb3af00adb22c6bb is not slashable", err)
+}
diff --git a/beacon-chain/core/blocks/testdata/beaconfuzz_91_beacon.ssz b/beacon-chain/core/blocks/testdata/beaconfuzz_91_beacon.ssz
new file mode 100644
index 000000000000..268ee8f0df38
Binary files /dev/null and b/beacon-chain/core/blocks/testdata/beaconfuzz_91_beacon.ssz differ
diff --git a/beacon-chain/core/blocks/testdata/beaconfuzz_91_proposer_slashing.ssz b/beacon-chain/core/blocks/testdata/beaconfuzz_91_proposer_slashing.ssz
new file mode 100644
index 000000000000..f7bdaca3ac00
Binary files /dev/null and b/beacon-chain/core/blocks/testdata/beaconfuzz_91_proposer_slashing.ssz differ