diff --git a/cli/multisig.go b/cli/multisig.go
index d88f5d963..f4b67e14d 100644
--- a/cli/multisig.go
+++ b/cli/multisig.go
@@ -878,6 +878,39 @@ var msigAddProposeCmd = &cli.Command{
 			from = defaddr
 		}
 
+		store := adt.WrapStore(ctx, cbor.NewCborStore(blockstore.NewAPIBlockstore(api)))
+
+		head, err := api.ChainHead(ctx)
+		if err != nil {
+			return err
+		}
+
+		act, err := api.StateGetActor(ctx, msig, head.Key())
+		if err != nil {
+			return err
+		}
+
+		mstate, err := multisig.Load(store, act)
+		if err != nil {
+			return err
+		}
+
+		signers, err := mstate.Signers()
+		if err != nil {
+			return err
+		}
+
+		addrId, err := api.StateLookupID(ctx, addr, types.EmptyTSK)
+		if err != nil {
+			return err
+		}
+
+		for _, s := range signers {
+			if s == addrId {
+				return fmt.Errorf("%s is already a signer", addr.String())
+			}
+		}
+
 		proto, err := api.MsigAddPropose(ctx, msig, from, addr, cctx.Bool("increase-threshold"))
 		if err != nil {
 			return err