diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e1a591b720..c77ef3b770 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -132,8 +132,8 @@ jobs:
 
       - name: Set environment variables
         run: |
-          mkdir -p target/tmp
-          echo "TMPDIR=$(pwd)/target/tmp" >> "$GITHUB_ENV"
+          mkdir -p target/tmp/deadbeefbee
+          echo "TMPDIR=$(pwd)/target/tmp/deadbeefbee" >> "$GITHUB_ENV"
           echo "GOMEMLIMIT=6GiB" >> "$GITHUB_ENV"
           echo "GOGC=80" >> "$GITHUB_ENV"
 
diff --git a/staker/block_validator.go b/staker/block_validator.go
index 108ef5710c..0ff74a8014 100644
--- a/staker/block_validator.go
+++ b/staker/block_validator.go
@@ -984,9 +984,12 @@ func (v *BlockValidator) checkLegacyValid() error {
 		log.Warn("legacy valid batch ahead of db", "current", batchCount, "required", requiredBatchCount)
 		return nil
 	}
-	msgCount, err := v.inboxTracker.GetBatchMessageCount(v.legacyValidInfo.AfterPosition.BatchNumber)
-	if err != nil {
-		return err
+	var msgCount arbutil.MessageIndex
+	if v.legacyValidInfo.AfterPosition.BatchNumber > 0 {
+		msgCount, err = v.inboxTracker.GetBatchMessageCount(v.legacyValidInfo.AfterPosition.BatchNumber - 1)
+		if err != nil {
+			return err
+		}
 	}
 	msgCount += arbutil.MessageIndex(v.legacyValidInfo.AfterPosition.PosInBatch)
 	processedCount, err := v.streamer.GetProcessedMessageCount()
diff --git a/system_tests/forwarder_test.go b/system_tests/forwarder_test.go
index 3691caf5d2..d4cf0d8eb7 100644
--- a/system_tests/forwarder_test.go
+++ b/system_tests/forwarder_test.go
@@ -7,6 +7,7 @@ import (
 	"context"
 	"fmt"
 	"math/big"
+	"os"
 	"path/filepath"
 	"strings"
 	"sync"
@@ -157,7 +158,18 @@ func createSequencer(
 
 // tmpPath returns file path with specified filename from temporary directory of the test.
 func tmpPath(t *testing.T, filename string) string {
-	return filepath.Join(t.TempDir(), filename)
+	t.Helper()
+	// create a unique, maximum 10 characters-long temporary directory {name} with path as $TMPDIR/{name}
+	tmpDir, err := os.MkdirTemp("", "")
+	if err != nil {
+		t.Fatalf("Failed to create temp dir: %v", err)
+	}
+	t.Cleanup(func() {
+		if err = os.RemoveAll(tmpDir); err != nil {
+			t.Errorf("Failed to cleanup temp dir: %v", err)
+		}
+	})
+	return filepath.Join(tmpDir, filename)
 }
 
 // testNodes creates specified number of paths for ipc from temporary directory of the test.