diff --git a/api/api_full.go b/api/api_full.go
index d0d87d943..c9afea021 100644
--- a/api/api_full.go
+++ b/api/api_full.go
@@ -241,6 +241,9 @@ type FullNode interface {
 	StateGetReceipt(context.Context, cid.Cid, types.TipSetKey) (*types.MessageReceipt, error)
 	StateMinerSectorCount(context.Context, address.Address, types.TipSetKey) (MinerSectors, error)
 	StateCompute(context.Context, abi.ChainEpoch, []*types.Message, types.TipSetKey) (*ComputeStateOutput, error)
+	// StateVerifiedClientStatus returns the data cap for the given address.
+	// Returns nil if there is no entry in the data cap table for the
+	// address.
 	StateVerifiedClientStatus(ctx context.Context, addr address.Address, tsk types.TipSetKey) (*verifreg.DataCap, error)
 
 	// MethodGroup: Msig