diff --git a/CHANGELOG.md b/CHANGELOG.md
index b37dca1c9b..3662b7b192 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,12 @@
 # Changelog
 
+## 0.29.1
+
+BUG FIXES
+
+* SDK
+  * [\#3207](https://github.com/cosmos/cosmos-sdk/issues/3207) - Fix token printing bug
+
 ## 0.29.0
 
 BREAKING CHANGES
diff --git a/types/coin.go b/types/coin.go
index 9742545324..1b353e6b43 100644
--- a/types/coin.go
+++ b/types/coin.go
@@ -140,8 +140,12 @@ func (coins Coins) IsValid() bool {
 	case 1:
 		return coins[0].IsPositive()
 	default:
-		lowDenom := coins[0].Denom
+		// check single coin case
+		if !(Coins{coins[0]}).IsValid() {
+			return false
+		}
 
+		lowDenom := coins[0].Denom
 		for _, coin := range coins[1:] {
 			if coin.Denom <= lowDenom {
 				return false
diff --git a/types/coin_test.go b/types/coin_test.go
index 774534860d..851d155155 100644
--- a/types/coin_test.go
+++ b/types/coin_test.go
@@ -251,8 +251,13 @@ func TestMinusCoins(t *testing.T) {
 
 func TestCoins(t *testing.T) {
 	good := Coins{
-		{"GAS", NewInt(1)},
-		{"MINERAL", NewInt(1)},
+		{"gas", NewInt(1)},
+		{"mineral", NewInt(1)},
+		{"tree", NewInt(1)},
+	}
+	mixedCase1 := Coins{
+		{"gAs", NewInt(1)},
+		{"MineraL", NewInt(1)},
 		{"TREE", NewInt(1)},
 	}
 	empty := Coins{
@@ -281,8 +286,13 @@ func TestCoins(t *testing.T) {
 		{"GAS", NewInt(1)},
 		{"MINERAL", NewInt(1)},
 	}
+	neg := Coins{
+		{"gas", NewInt(-1)},
+		{"mineral", NewInt(1)},
+	}
 
 	assert.True(t, good.IsValid(), "Coins are valid")
+	assert.False(t, mixedCase1.IsValid(), "Coins denoms contain upper case characters")
 	assert.True(t, good.IsPositive(), "Expected coins to be positive: %v", good)
 	assert.False(t, null.IsPositive(), "Expected coins to not be positive: %v", null)
 	assert.True(t, good.IsAllGTE(empty), "Expected %v to be >= %v", good, empty)
@@ -292,6 +302,7 @@ func TestCoins(t *testing.T) {
 	assert.False(t, badSort2.IsValid(), "Coins are not sorted")
 	assert.False(t, badAmt.IsValid(), "Coins cannot include 0 amounts")
 	assert.False(t, dup.IsValid(), "Duplicate coin")
+	assert.False(t, neg.IsValid(), "Negative first-denom coin")
 }
 
 func TestCoinsGT(t *testing.T) {
diff --git a/x/bank/keeper.go b/x/bank/keeper.go
index 706f445eb9..1a11631ca6 100644
--- a/x/bank/keeper.go
+++ b/x/bank/keeper.go
@@ -194,8 +194,13 @@ func addCoins(ctx sdk.Context, am auth.AccountKeeper, addr sdk.AccAddress, amt s
 }
 
 // SendCoins moves coins from one account to another
-// NOTE: Make sure to revert state changes from tx on error
 func sendCoins(ctx sdk.Context, am auth.AccountKeeper, fromAddr sdk.AccAddress, toAddr sdk.AccAddress, amt sdk.Coins) (sdk.Tags, sdk.Error) {
+	// Safety check ensuring that when sending coins the keeper must maintain the
+	// supply invariant.
+	if !amt.IsValid() {
+		return nil, sdk.ErrInvalidCoins(amt.String())
+	}
+
 	_, subTags, err := subtractCoins(ctx, am, fromAddr, amt)
 	if err != nil {
 		return nil, err
@@ -212,6 +217,12 @@ func sendCoins(ctx sdk.Context, am auth.AccountKeeper, fromAddr sdk.AccAddress,
 // InputOutputCoins handles a list of inputs and outputs
 // NOTE: Make sure to revert state changes from tx on error
 func inputOutputCoins(ctx sdk.Context, am auth.AccountKeeper, inputs []Input, outputs []Output) (sdk.Tags, sdk.Error) {
+	// Safety check ensuring that when sending coins the keeper must maintain the
+	// supply invariant.
+	if err := ValidateInputsOutputs(inputs, outputs); err != nil {
+		return nil, err
+	}
+
 	allTags := sdk.EmptyTags()
 
 	for _, in := range inputs {
diff --git a/x/bank/keeper_test.go b/x/bank/keeper_test.go
index 14f40f9c4f..4563038317 100644
--- a/x/bank/keeper_test.go
+++ b/x/bank/keeper_test.go
@@ -13,7 +13,6 @@ import (
 	codec "github.com/cosmos/cosmos-sdk/codec"
 	"github.com/cosmos/cosmos-sdk/store"
 	sdk "github.com/cosmos/cosmos-sdk/types"
-
 	"github.com/cosmos/cosmos-sdk/x/auth"
 )
 
@@ -108,7 +107,6 @@ func TestKeeper(t *testing.T) {
 	require.True(t, bankKeeper.GetCoins(ctx, addr).IsEqual(sdk.Coins{sdk.NewInt64Coin("barcoin", 21), sdk.NewInt64Coin("foocoin", 4)}))
 	require.True(t, bankKeeper.GetCoins(ctx, addr2).IsEqual(sdk.Coins{sdk.NewInt64Coin("barcoin", 7), sdk.NewInt64Coin("foocoin", 6)}))
 	require.True(t, bankKeeper.GetCoins(ctx, addr3).IsEqual(sdk.Coins{sdk.NewInt64Coin("barcoin", 2), sdk.NewInt64Coin("foocoin", 5)}))
-
 }
 
 func TestSendKeeper(t *testing.T) {
@@ -146,8 +144,8 @@ func TestSendKeeper(t *testing.T) {
 	require.True(t, sendKeeper.GetCoins(ctx, addr).IsEqual(sdk.Coins{sdk.NewInt64Coin("foocoin", 10)}))
 	require.True(t, sendKeeper.GetCoins(ctx, addr2).IsEqual(sdk.Coins{sdk.NewInt64Coin("foocoin", 5)}))
 
-	_, err2 := sendKeeper.SendCoins(ctx, addr, addr2, sdk.Coins{sdk.NewInt64Coin("foocoin", 50)})
-	assert.Implements(t, (*sdk.Error)(nil), err2)
+	_, err := sendKeeper.SendCoins(ctx, addr, addr2, sdk.Coins{sdk.NewInt64Coin("foocoin", 50)})
+	require.Implements(t, (*sdk.Error)(nil), err)
 	require.True(t, sendKeeper.GetCoins(ctx, addr).IsEqual(sdk.Coins{sdk.NewInt64Coin("foocoin", 10)}))
 	require.True(t, sendKeeper.GetCoins(ctx, addr2).IsEqual(sdk.Coins{sdk.NewInt64Coin("foocoin", 5)}))
 
@@ -156,6 +154,11 @@ func TestSendKeeper(t *testing.T) {
 	require.True(t, sendKeeper.GetCoins(ctx, addr).IsEqual(sdk.Coins{sdk.NewInt64Coin("barcoin", 20), sdk.NewInt64Coin("foocoin", 5)}))
 	require.True(t, sendKeeper.GetCoins(ctx, addr2).IsEqual(sdk.Coins{sdk.NewInt64Coin("barcoin", 10), sdk.NewInt64Coin("foocoin", 10)}))
 
+	// validate coins with invalid denoms or negative values cannot be sent
+	// NOTE: We must use the Coin literal as the constructor does not allow
+	// negative values.
+	_, err = sendKeeper.SendCoins(ctx, addr, addr2, sdk.Coins{sdk.Coin{"FOOCOIN", sdk.NewInt(-5)}})
+	require.Error(t, err)
 }
 
 func TestViewKeeper(t *testing.T) {
diff --git a/x/bank/msgs.go b/x/bank/msgs.go
index 48d251a1f8..74705ebc74 100644
--- a/x/bank/msgs.go
+++ b/x/bank/msgs.go
@@ -37,25 +37,8 @@ func (msg MsgSend) ValidateBasic() sdk.Error {
 	if len(msg.Outputs) == 0 {
 		return ErrNoOutputs(DefaultCodespace).TraceSDK("")
 	}
-	// make sure all inputs and outputs are individually valid
-	var totalIn, totalOut sdk.Coins
-	for _, in := range msg.Inputs {
-		if err := in.ValidateBasic(); err != nil {
-			return err.TraceSDK("")
-		}
-		totalIn = totalIn.Plus(in.Coins)
-	}
-	for _, out := range msg.Outputs {
-		if err := out.ValidateBasic(); err != nil {
-			return err.TraceSDK("")
-		}
-		totalOut = totalOut.Plus(out.Coins)
-	}
-	// make sure inputs and outputs match
-	if !totalIn.IsEqual(totalOut) {
-		return sdk.ErrInvalidCoins(totalIn.String()).TraceSDK("inputs and outputs don't match")
-	}
-	return nil
+
+	return ValidateInputsOutputs(msg.Inputs, msg.Outputs)
 }
 
 // Implements Msg.
@@ -170,3 +153,33 @@ func NewOutput(addr sdk.AccAddress, coins sdk.Coins) Output {
 	}
 	return output
 }
+
+// ----------------------------------------------------------------------------
+// Auxiliary
+
+// ValidateInputsOutputs validates that each respective input and output is
+// valid and that the sum of inputs is equal to the sum of outputs.
+func ValidateInputsOutputs(inputs []Input, outputs []Output) sdk.Error {
+	var totalIn, totalOut sdk.Coins
+
+	for _, in := range inputs {
+		if err := in.ValidateBasic(); err != nil {
+			return err.TraceSDK("")
+		}
+		totalIn = totalIn.Plus(in.Coins)
+	}
+
+	for _, out := range outputs {
+		if err := out.ValidateBasic(); err != nil {
+			return err.TraceSDK("")
+		}
+		totalOut = totalOut.Plus(out.Coins)
+	}
+
+	// make sure inputs and outputs match
+	if !totalIn.IsEqual(totalOut) {
+		return sdk.ErrInvalidCoins(totalIn.String()).TraceSDK("inputs and outputs don't match")
+	}
+
+	return nil
+}