diff --git a/x/oracle/abci_test.go b/x/oracle/abci_test.go
index 78b4fa05..10f7aea5 100644
--- a/x/oracle/abci_test.go
+++ b/x/oracle/abci_test.go
@@ -7,6 +7,7 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/require"
+	"github.com/tendermint/tendermint/libs/rand"
 
 	sdk "github.com/cosmos/cosmos-sdk/types"
 	stakingtypes "github.com/cosmos/cosmos-sdk/x/staking/types"
@@ -335,14 +336,14 @@ func TestOracleExchangeRate(t *testing.T) {
 	input, h := setup(t)
 
 	krwRandomExchangeRate := sdk.NewDecWithPrec(1000000000, int64(6)).MulInt64(core.MicroUnit)
-	uswRandomExchangeRate := sdk.NewDecWithPrec(1000000, int64(6)).MulInt64(core.MicroUnit)
+	usdRandomExchangeRate := sdk.NewDecWithPrec(1000000, int64(6)).MulInt64(core.MicroUnit)
 
 	// KRW has been chosen as referenceTerra by highest voting power
 	// Account 1, USD, KRW
-	makeAggregatePrevoteAndVote(t, input, h, 0, sdk.DecCoins{{Denom: core.MicroUSDDenom, Amount: uswRandomExchangeRate}, {Denom: core.MicroKRWDenom, Amount: krwRandomExchangeRate}}, 0)
+	makeAggregatePrevoteAndVote(t, input, h, 0, sdk.DecCoins{{Denom: core.MicroUSDDenom, Amount: usdRandomExchangeRate}, {Denom: core.MicroKRWDenom, Amount: krwRandomExchangeRate}}, 0)
 
 	// Account 2, USD, KRW
-	makeAggregatePrevoteAndVote(t, input, h, 0, sdk.DecCoins{{Denom: core.MicroUSDDenom, Amount: uswRandomExchangeRate}, {Denom: core.MicroKRWDenom, Amount: krwRandomExchangeRate}}, 1)
+	makeAggregatePrevoteAndVote(t, input, h, 0, sdk.DecCoins{{Denom: core.MicroUSDDenom, Amount: usdRandomExchangeRate}, {Denom: core.MicroKRWDenom, Amount: krwRandomExchangeRate}}, 1)
 
 	// Account 3, KRW, SDR
 	makeAggregatePrevoteAndVote(t, input, h, 0, sdk.DecCoins{{Denom: core.MicroKRWDenom, Amount: krwRandomExchangeRate}, {Denom: core.MicroSDRDenom, Amount: randomExchangeRate}}, 2)
@@ -364,6 +365,34 @@ func TestOracleExchangeRate(t *testing.T) {
 	require.Equal(t, expectedRewardAmt2, rewards.Rewards.AmountOf(core.MicroLunaDenom).TruncateInt())
 }
 
+func TestOracleEnsureSorted(t *testing.T) {
+	input, h := setup(t)
+
+	for i := 0; i < 100; i++ {
+		krwExchangeRate1 := sdk.NewDecWithPrec(int64(rand.Uint64()%100000000), 6).MulInt64(core.MicroUnit)
+		usdExchangeRate1 := sdk.NewDecWithPrec(int64(rand.Uint64()%100000000), 6).MulInt64(core.MicroUnit)
+
+		krwExchangeRate2 := sdk.NewDecWithPrec(int64(rand.Uint64()%100000000), 6).MulInt64(core.MicroUnit)
+		usdExchangeRate2 := sdk.NewDecWithPrec(int64(rand.Uint64()%100000000), 6).MulInt64(core.MicroUnit)
+
+		krwExchangeRate3 := sdk.NewDecWithPrec(int64(rand.Uint64()%100000000), 6).MulInt64(core.MicroUnit)
+		usdExchangeRate3 := sdk.NewDecWithPrec(int64(rand.Uint64()%100000000), 6).MulInt64(core.MicroUnit)
+
+		// Account 1, USD, KRW
+		makeAggregatePrevoteAndVote(t, input, h, 0, sdk.DecCoins{{Denom: core.MicroUSDDenom, Amount: usdExchangeRate1}, {Denom: core.MicroKRWDenom, Amount: krwExchangeRate1}}, 0)
+
+		// Account 2, USD, KRW
+		makeAggregatePrevoteAndVote(t, input, h, 0, sdk.DecCoins{{Denom: core.MicroUSDDenom, Amount: usdExchangeRate2}, {Denom: core.MicroKRWDenom, Amount: krwExchangeRate2}}, 1)
+
+		// Account 3, USD, KRW
+		makeAggregatePrevoteAndVote(t, input, h, 0, sdk.DecCoins{{Denom: core.MicroUSDDenom, Amount: krwExchangeRate3}, {Denom: core.MicroKRWDenom, Amount: usdExchangeRate3}}, 2)
+
+		require.NotPanics(t, func() {
+			oracle.EndBlocker(input.Ctx.WithBlockHeight(1), input.OracleKeeper)
+		})
+	}
+}
+
 func TestOracleExchangeRateVal5(t *testing.T) {
 	input, h := setupVal5(t)
 
diff --git a/x/oracle/types/ballot.go b/x/oracle/types/ballot.go
index 313d3451..f65cfbb8 100644
--- a/x/oracle/types/ballot.go
+++ b/x/oracle/types/ballot.go
@@ -3,6 +3,7 @@ package types
 import (
 	"fmt"
 	"math"
+	"sort"
 	"strconv"
 
 	sdk "github.com/cosmos/cosmos-sdk/types"
@@ -60,6 +61,7 @@ func (pb ExchangeRateBallot) ToCrossRate(bases map[string]sdk.Dec) (cb ExchangeR
 		cb = append(cb, vote)
 	}
 
+	sort.Sort(cb)
 	return
 }
 
@@ -76,6 +78,10 @@ func (pb ExchangeRateBallot) Power() int64 {
 // WeightedMedian returns the median weighted by the power of the ExchangeRateVote.
 // CONTRACT: ballot must be sorted
 func (pb ExchangeRateBallot) WeightedMedian() sdk.Dec {
+	if !sort.IsSorted(pb) {
+		panic("ballot must be sorted")
+	}
+
 	totalPower := pb.Power()
 	if pb.Len() > 0 {
 		pivot := int64(0)
diff --git a/x/oracle/types/ballot_test.go b/x/oracle/types/ballot_test.go
index 1f2c74a0..bea8cdad 100644
--- a/x/oracle/types/ballot_test.go
+++ b/x/oracle/types/ballot_test.go
@@ -3,6 +3,7 @@ package types
 import (
 	"fmt"
 	"math"
+	"sort"
 	"strconv"
 
 	"testing"
@@ -103,6 +104,8 @@ func TestToCrossRate(t *testing.T) {
 		}
 	}
 
+	sort.Sort(cb)
+
 	baseMapBallot := pbBase.ToMap()
 	require.Equal(t, cb, pbQuote.ToCrossRate(baseMapBallot))
 }