diff --git a/privval/file.go b/privval/file.go
index 213e1760e..cefbef376 100644
--- a/privval/file.go
+++ b/privval/file.go
@@ -369,6 +369,7 @@ func (pv *FilePV) signVote(chainID string, vote *tmproto.Vote) error {
 	}
 
 	signBytes := types.VoteSignBytes(chainID, vote)
+	extSignBytes := types.VoteExtensionSignBytes(chainID, vote)
 
 	// We might crash before writing to the wal,
 	// causing us to try to re-sign for the same HRS.
@@ -398,18 +399,15 @@ func (pv *FilePV) signVote(chainID string, vote *tmproto.Vote) error {
 	if err != nil {
 		return err
 	}
-	if err = pv.saveSigned(height, round, step, signBytes, sig); err != nil {
+	if err := pv.saveSigned(height, round, step, signBytes, sig); err != nil {
 		return err
 	}
 	vote.Signature = sig
 
-	// Sign the vote extension, if any
-	if len(vote.Extension) > 0 {
-		var err error
-		vote.ExtensionSignature, err = pv.Key.PrivKey.Sign(vote.Extension)
-		if err != nil {
-			return err
-		}
+	// Sign the vote extension, regardless of whether it's present or not
+	vote.ExtensionSignature, err = pv.Key.PrivKey.Sign(extSignBytes)
+	if err != nil {
+		return err
 	}
 
 	return nil
diff --git a/types/canonical.go b/types/canonical.go
index 83250ae1e..203e70108 100644
--- a/types/canonical.go
+++ b/types/canonical.go
@@ -65,6 +65,19 @@ func CanonicalizeVote(chainID string, vote *tmproto.Vote) tmproto.CanonicalVote
 	}
 }
 
+// CanonicalizeVoteExtension extracts the vote extension from the given vote
+// and constructs a CanonicalizeVoteExtension struct, whose representation in
+// bytes is what is signed in order to produce the vote extension's signature.
+func CanonicalizeVoteExtension(chainID string, vote *tmproto.Vote) tmproto.CanonicalVoteExtension {
+	return tmproto.CanonicalVoteExtension{
+		Extension: vote.Extension,
+		Height:    vote.Height,
+		Round:     vote.Round,
+		ChainId:   chainID,
+		Address:   vote.ValidatorAddress,
+	}
+}
+
 // CanonicalTime can be used to stringify time in a canonical way.
 func CanonicalTime(t time.Time) string {
 	// Note that sending time over amino resets it to
diff --git a/types/priv_validator.go b/types/priv_validator.go
index a67e23779..06aaa9334 100644
--- a/types/priv_validator.go
+++ b/types/priv_validator.go
@@ -90,16 +90,15 @@ func (pv MockPV) SignVote(ctx context.Context, chainID string, vote *tmproto.Vot
 	}
 
 	signBytes := VoteSignBytes(useChainID, vote)
+	extSignBytes := VoteExtensionSignBytes(useChainID, vote)
 	sig, err := pv.PrivKey.Sign(signBytes)
 	if err != nil {
 		return err
 	}
 	vote.Signature = sig
-	if len(vote.Extension) > 0 {
-		vote.ExtensionSignature, err = pv.PrivKey.Sign(vote.Extension)
-		if err != nil {
-			return err
-		}
+	vote.ExtensionSignature, err = pv.PrivKey.Sign(extSignBytes)
+	if err != nil {
+		return err
 	}
 	return nil
 }
diff --git a/types/vote.go b/types/vote.go
index ea205aa3a..301b5c8ba 100644
--- a/types/vote.go
+++ b/types/vote.go
@@ -103,6 +103,21 @@ func VoteSignBytes(chainID string, vote *tmproto.Vote) []byte {
 	return bz
 }
 
+// VoteExtensionSignBytes returns the proto-encoding of the canonicalized vote
+// extension for signing. Panics if the marshaling fails.
+//
+// Similar to VoteSignBytes, the encoded Protobuf message is varint
+// length-prefixed for backwards-compatibility with the Amino encoding.
+func VoteExtensionSignBytes(chainID string, vote *tmproto.Vote) []byte {
+	pb := CanonicalizeVoteExtension(chainID, vote)
+	bz, err := protoio.MarshalDelimited(&pb)
+	if err != nil {
+		panic(err)
+	}
+
+	return bz
+}
+
 func (vote *Vote) Copy() *Vote {
 	voteCopy := *vote
 	return &voteCopy