diff --git a/math/CHANGELOG.md b/math/CHANGELOG.md
index 43e36e120b..3d97302b88 100644
--- a/math/CHANGELOG.md
+++ b/math/CHANGELOG.md
@@ -34,6 +34,12 @@ Ref: https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.j
 
 # Changelog
 
+## [Unreleased] 
+
+### Bug Fixes
+
+* [#15506](https://github.com/cosmos/cosmos-sdk/issues/16605) fix: Dec marshal shouldn't have side effects
+
 ## [math/v1.0.0-rc.0](https://github.com/cosmos/cosmos-sdk/releases/tag/math/v1.0.0-rc.0) - 2023-03-13
 
 ### Features
@@ -43,6 +49,7 @@ Ref: https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.j
 ### Bug Fixes
 
 * [#14922](https://github.com/cosmos/cosmos-sdk/issues/14922) check for negative precision
+* [#15506](https://github.com/cosmos/cosmos-sdk/issues/16605) fix: Dec marshal shouldn't have side effects
 
 ### Testing
 
diff --git a/math/dec.go b/math/dec.go
index 844b3039af..8875dfdd70 100644
--- a/math/dec.go
+++ b/math/dec.go
@@ -799,19 +799,21 @@ func (d LegacyDec) MarshalYAML() (interface{}, error) {
 
 // Marshal implements the gogo proto custom type interface.
 func (d LegacyDec) Marshal() ([]byte, error) {
-	if d.i == nil {
-		d.i = new(big.Int)
+	i := d.i
+	if i == nil {
+		i = new(big.Int)
 	}
-	return d.i.MarshalText()
+	return i.MarshalText()
 }
 
 // MarshalTo implements the gogo proto custom type interface.
 func (d *LegacyDec) MarshalTo(data []byte) (n int, err error) {
-	if d.i == nil {
-		d.i = new(big.Int)
+	i := d.i
+	if i == nil {
+		i = new(big.Int)
 	}
 
-	if d.i.Cmp(zeroInt) == 0 {
+	if i.Cmp(zeroInt) == 0 {
 		copy(data, []byte{0x30})
 		return 1, nil
 	}
diff --git a/tests/integration/aminojson/aminojson_test.go b/tests/integration/aminojson/aminojson_test.go
index ad8168a0fe..0a2abe15f3 100644
--- a/tests/integration/aminojson/aminojson_test.go
+++ b/tests/integration/aminojson/aminojson_test.go
@@ -665,6 +665,26 @@ func TestSendAuthorization(t *testing.T) {
 	require.Equal(t, string(legacyAminoJson), string(aminoJson))
 }
 
+func TestDecimalMutation(t *testing.T) {
+	encCfg := testutil.MakeTestEncodingConfig(staking.AppModuleBasic{})
+	rates := &stakingtypes.CommissionRates{}
+	rateBz, _ := encCfg.Amino.MarshalJSON(rates)
+	require.Equal(t, `{"rate":"0","max_rate":"0","max_change_rate":"0"}`, string(rateBz))
+	_, err := gogoproto.Marshal(rates)
+	require.NoError(t, err)
+	rateBz, _ = encCfg.Amino.MarshalJSON(rates)
+
+	// these assertions show behavior prior to the merge of https://github.com/cosmos/cosmos-sdk/pull/15506
+	// and should be updated to reflect the new behavior once a release of math is made and updated in ./tests/go.mod
+	require.NotEqual(t, `{"rate":"0","max_rate":"0","max_change_rate":"0"}`, string(rateBz))
+	require.Equal(t,
+		`{"rate":"0.000000000000000000","max_rate":"0.000000000000000000","max_change_rate":"0.000000000000000000"}`,
+		string(rateBz))
+
+	// new behavior
+	//require.Equal(t, `{"rate":"0","max_rate":"0","max_change_rate":"0"}`, string(rateBz))
+}
+
 func postFixPulsarMessage(msg proto.Message) {
 	switch m := msg.(type) {
 	case *authapi.ModuleAccount: