diff --git a/CHANGELOG.md b/CHANGELOG.md
index 77b0401c5261..9e152f9200d2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -61,6 +61,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
   
 ### Bug Fixes
 
+* (x/slashing) [#18016](https://github.com/cosmos/cosmos-sdk/pull/18016) Fixed builder function for missed blocks key (`validatorMissedBlockBitArrayPrefixKey`) in slashing/migration/v4
 * (x/gov) [#17873](https://github.com/cosmos/cosmos-sdk/pull/17873) Fail any inactive and active proposals whose messages cannot be decoded.
 
 ### API Breaking Changes
diff --git a/x/slashing/migrations/v4/keys.go b/x/slashing/migrations/v4/keys.go
index 1ac42b6c1aff..c5ab30ff72bd 100644
--- a/x/slashing/migrations/v4/keys.go
+++ b/x/slashing/migrations/v4/keys.go
@@ -28,7 +28,7 @@ func ValidatorSigningInfoAddress(key []byte) (v sdk.ConsAddress) {
 }
 
 func validatorMissedBlockBitArrayPrefixKey(v sdk.ConsAddress) []byte {
-	return append(validatorMissedBlockBitArrayKeyPrefix, v.Bytes()...)
+	return append(validatorMissedBlockBitArrayKeyPrefix, address.MustLengthPrefix(v.Bytes())...)
 }
 
 func ValidatorMissedBlockBitArrayKey(v sdk.ConsAddress, i int64) []byte {
diff --git a/x/slashing/migrations/v4/migrate_test.go b/x/slashing/migrations/v4/migrate_test.go
index 844de3e900ed..fc8a043610b9 100644
--- a/x/slashing/migrations/v4/migrate_test.go
+++ b/x/slashing/migrations/v4/migrate_test.go
@@ -41,10 +41,6 @@ func TestMigrate(t *testing.T) {
 	err := v4.Migrate(ctx, cdc, store, params)
 	require.NoError(t, err)
 
-	// ensure old entries no longer exist and new bitmap chunk entries exist
-	entries := v4.GetValidatorMissedBlocks(ctx, cdc, store, consAddr, params)
-	require.Empty(t, entries)
-
 	for i := int64(0); i < params.SignedBlocksWindow; i++ {
 		chunkIndex := i / v4.MissedBlockBitmapChunkSize
 		chunk := store.Get(v4.ValidatorMissedBlockBitmapKey(consAddr, chunkIndex))