diff --git a/CHANGELOG.md b/CHANGELOG.md
index 554c72a36fcc..c9f009c0a82e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -57,6 +57,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 ### Bug Fixes
 
 * [\#9969](https://github.com/cosmos/cosmos-sdk/pull/9969) fix: use keyring in config for add-genesis-account cmd.
+* [\#10061](https://github.com/cosmos/cosmos-sdk/pull/10061) Ensure that `LegacyAminoPubKey` struct correctly unmarshals from JSON
 
 ### Client Breaking Changes
 
@@ -64,7 +65,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 ### API Breaking Changes
 
-* [\#10077](https://github.com/cosmos/cosmos-sdk/pull/10077) Remove telemetry on `GasKV` and `CacheKV` store Get/Set operations, significantly improving their performance.
++ [\#10077](https://github.com/cosmos/cosmos-sdk/pull/10077) Remove telemetry on `GasKV` and `CacheKV` store Get/Set operations, significantly improving their performance.
 
 ## [v0.42.9](https://github.com/cosmos/cosmos-sdk/releases/tag/v0.42.9) - 2021-08-04
 
diff --git a/crypto/keys/multisig/amino.go b/crypto/keys/multisig/amino.go
index 4849a23173d2..641fe1f691a7 100644
--- a/crypto/keys/multisig/amino.go
+++ b/crypto/keys/multisig/amino.go
@@ -78,9 +78,28 @@ func (m *LegacyAminoPubKey) UnmarshalAminoJSON(tmPk tmMultisig) error {
 	// Instead of just doing `*m = *protoPk`, we prefer to modify in-place the
 	// existing Anys inside `m` (instead of allocating new Anys), as so not to
 	// break the `.compat` fields in the existing Anys.
+	if m.PubKeys == nil {
+		m.PubKeys = make([]*types.Any, len(tmPk.PubKeys))
+	}
 	for i := range m.PubKeys {
-		m.PubKeys[i].TypeUrl = protoPk.PubKeys[i].TypeUrl
-		m.PubKeys[i].Value = protoPk.PubKeys[i].Value
+		if m.PubKeys[i] == nil {
+			// create the compat jsonBz value
+			bz, err := AminoCdc.MarshalJSON(tmPk.PubKeys[i])
+			if err != nil {
+				return err
+			}
+
+			m.PubKeys[i] = protoPk.PubKeys[i]
+			// UnmarshalJSON():
+			// just sets the compat.jsonBz value.
+			// always succeeds: err == nil
+			if err := m.PubKeys[i].UnmarshalJSON(bz); err != nil {
+				return err
+			}
+		} else {
+			m.PubKeys[i].TypeUrl = protoPk.PubKeys[i].TypeUrl
+			m.PubKeys[i].Value = protoPk.PubKeys[i].Value
+		}
 	}
 	m.Threshold = protoPk.Threshold
 
diff --git a/crypto/keys/multisig/multisig_test.go b/crypto/keys/multisig/multisig_test.go
index 1284c6c88476..0285ae0ef9ae 100644
--- a/crypto/keys/multisig/multisig_test.go
+++ b/crypto/keys/multisig/multisig_test.go
@@ -17,6 +17,15 @@ import (
 	"github.com/cosmos/cosmos-sdk/x/auth/legacy/legacytx"
 )
 
+func generatePubKeys(n int) []cryptotypes.PubKey {
+	pks := make([]cryptotypes.PubKey, n)
+	for i := 0; i < n; i++ {
+		pks[i] = secp256k1.GenPrivKey().PubKey()
+	}
+
+	return pks
+}
+
 func TestAddress(t *testing.T) {
 	msg := []byte{1, 2, 3, 4}
 	pubKeys, _ := generatePubKeysAndSignatures(5, msg)
@@ -379,5 +388,32 @@ func TestAminoUnmarshalJSON(t *testing.T) {
 	var pk cryptotypes.PubKey
 	err := cdc.UnmarshalJSON([]byte(pkJSON), &pk)
 	require.NoError(t, err)
-	require.Equal(t, uint32(3), pk.(*kmultisig.LegacyAminoPubKey).Threshold)
+	lpk := pk.(*kmultisig.LegacyAminoPubKey)
+	require.Equal(t, uint32(3), lpk.Threshold)
+	require.Equal(t, 5, len(pk.(*kmultisig.LegacyAminoPubKey).PubKeys))
+
+	for _, key := range pk.(*kmultisig.LegacyAminoPubKey).PubKeys {
+		require.NotNil(t, key)
+		pk := secp256k1.PubKey{}
+		err := pk.Unmarshal(key.Value)
+		require.NoError(t, err)
+	}
+}
+
+func TestProtoMarshalJSON(t *testing.T) {
+	require := require.New(t)
+	pubkeys := generatePubKeys(3)
+	msig := kmultisig.NewLegacyAminoPubKey(2, pubkeys)
+
+	registry := types.NewInterfaceRegistry()
+	cryptocodec.RegisterInterfaces(registry)
+	cdc := codec.NewProtoCodec(registry)
+
+	bz, err := cdc.MarshalInterfaceJSON(msig)
+	require.NoError(err)
+
+	var pk2 cryptotypes.PubKey
+	err = cdc.UnmarshalInterfaceJSON(bz, &pk2)
+	require.NoError(err)
+	require.True(pk2.Equals(msig))
 }