diff --git a/src/frontend/apiserver/backend/convert_pure.go b/src/frontend/apiserver/backend/convert_pure.go
index 535c553b..20d4ca49 100644
--- a/src/frontend/apiserver/backend/convert_pure.go
+++ b/src/frontend/apiserver/backend/convert_pure.go
@@ -10,7 +10,7 @@ import (
 //
 //	|63     62|61        56|55       52|51         20|19      15|14          0|
 //	|  TAG   | CLUSTER_ID | APISERVER_ID| TIMESTAMP  | SEQ_HIGH  | ARRAY_IDX  |
-//	| 2 bits | 6 bits     | 4 bits      | 32 bits    | 15 bits   | 15 bits     |
+//	| 2 bits | 6 bits     | 4 bits      | 32 bits    | 5 bits    | 15 bits     |
 const (
 	nTagBits          = 2
 	tagShift          = 62
@@ -21,8 +21,8 @@ const (
 	nTimestampBits    = 32
 	timestampShift    = 20
 	nArrayIdxBits     = 15
-	sequenceHighShift = 15   // mirrors SEQUENCE_HIGH_SHIFT in config.h
-	nSequenceBits     = 30   // mirrors N_SEQUENCE_BITS in config.h
+	sequenceHighShift = 15   // mirrors SEQUENCE_HIGH_SHIFT in config.h (== N_ARRAY_IDX_BITS)
+	nSequenceBits     = 20   // N_JOBID_BITS(64) - N_CLUSTER_ID_BITS(6) - N_APISERVER_ID_BITS(4) - N_TIMESTAMP_BITS(32) - N_TAG_BITS(2) = 20
 	tagJobArray       = 0x01 // mirrors TAG_JOB_ARRAY in config.h
 )
 
diff --git a/src/frontend/apiserver/backend/convert_test.go b/src/frontend/apiserver/backend/convert_test.go
index 3eaa847c..b18ff635 100644
--- a/src/frontend/apiserver/backend/convert_test.go
+++ b/src/frontend/apiserver/backend/convert_test.go
@@ -367,6 +367,42 @@ func TestRawJobToModel_ArrayChildrenShareBaseID(t *testing.T) {
 	}
 }
 
+// TestExtractArrayBaseID_LargeTimestamp verifies that ExtractArrayBaseID does not
+// leak timestamp bits into the extracted sequence when the timestamp field has
+// large values. This would fail with nSequenceBits=30 (extracts 15 bits from
+// position 15, bleeding into the timestamp at bits 20-51) but passes with the
+// correct nSequenceBits=20 (extracts 5 bits from position 15).
+func TestExtractArrayBaseID_LargeTimestamp(t *testing.T) {
+	jobNumber := uint64(7)
+	arrayIdx := uint64(3)
+	sequence := jobNumber<<sequenceHighShift + arrayIdx
+	// Use a typical Unix-epoch timestamp (bits 20-51 should stay in timestamp)
+	id := makeJobID(1, 0, 1714560000, tagJobArray, sequence)
+
+	base := ExtractArrayBaseID(id)
+	// The base ID must have the same cluster, apiserver, and timestamp —
+	// no timestamp bits should leak into the sequence field.
+	gotCluster := extractBits(base, clusterIDShift, nClusterIDBits)
+	gotApiserver := extractBits(base, apiserverIDShift, nApiserverIDBits)
+	gotTimestamp := extractBits(base, timestampShift, nTimestampBits)
+
+	if gotCluster != 1 {
+		t.Errorf("cluster ID leaked: got %d, want 1", gotCluster)
+	}
+	if gotApiserver != 0 {
+		t.Errorf("apiserver ID leaked: got %d, want 0", gotApiserver)
+	}
+	if gotTimestamp != 1714560000 {
+		t.Errorf("timestamp corrupted: got %d, want 1714560000", gotTimestamp)
+	}
+
+	// The base ID's sequence should be just jobNumber<<sequenceHighShift (idx=0, tag=0)
+	expectedBase := makeJobID(1, 0, 1714560000, 0, jobNumber<<sequenceHighShift)
+	if base != expectedBase {
+		t.Errorf("base ID mismatch with large timestamp: got %d, want %d", base, expectedBase)
+	}
+}
+
 func TestIsArrayJob(t *testing.T) {
 	// Non-array job (tag=0x00): IsArrayJob returns false
 	nonArrayID := makeJobID(1, 0, 1700000000, 0, 5)