diff --git a/specs/bls_signature.md b/specs/bls_signature.md
index b0490b7ae..14a4f1cb7 100644
--- a/specs/bls_signature.md
+++ b/specs/bls_signature.md
@@ -110,11 +110,11 @@ def modular_squareroot(value: Fq2) -> Fq2:
 
 ### `bls_aggregate_pubkeys`
 
-Let `bls_aggregate_pubkeys(pubkeys: List[Bytes48]) -> Bytes48` return `pubkeys[0] + .... + pubkeys[len(pubkeys)-1]`, where `+` is the elliptic curve addition operation over the G1 curve.
+Let `bls_aggregate_pubkeys(pubkeys: List[Bytes48]) -> Bytes48` return `pubkeys[0] + .... + pubkeys[len(pubkeys)-1]`, where `+` is the elliptic curve addition operation over the G1 curve. (When `len(pubkeys) == 0` the empty sum is the G1 point at infinity.)
 
 ### `bls_aggregate_signatures`
 
-Let `bls_aggregate_signatures(signatures: List[Bytes96]) -> Bytes96` return `signatures[0] + .... + signatures[len(signatures)-1]`, where `+` is the elliptic curve addition operation over the G2 curve.
+Let `bls_aggregate_signatures(signatures: List[Bytes96]) -> Bytes96` return `signatures[0] + .... + signatures[len(signatures)-1]`, where `+` is the elliptic curve addition operation over the G2 curve. (When `len(signatures) == 0` the empty sum is the G2 point at infinity.)
 
 ## Signature verification