diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 88f43ccbb8..c9185b8f74 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -40,6 +40,7 @@ The sandbox cluster installation is running under the constant load generated by
 * BUGFIX: [MetricsQL](https://docs.victoriametrics.com/MetricsQL.html): properly propagate [label filters](https://docs.victoriametrics.com/keyconcepts/#filtering) from multiple arguments passed to [aggregate functions](https://docs.victoriametrics.com/metricsql/#aggregate-functions). For example, `sum({job="foo"}, {job="bar"}) by (job) + a` was improperly optimized to `sum({job="foo"}, {job="bar"}) by (job) + a{job="foo"}` before being executed. This could lead to unexpected results. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5604).
 * BUGFIX: [MetricsQL](https://docs.victoriametrics.com/MetricsQL.html): properly handle precision errors when calculating [changes](https://docs.victoriametrics.com/metricsql/#changes), [changes_prometheus](https://docs.victoriametrics.com/metricsql/#changes_prometheus), [increases_over_time](https://docs.victoriametrics.com/metricsql/#increases_over_time) and [resets](https://docs.victoriametrics.com/metricsql/#resets) functions. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/767).
 * BUGFIX: all VictoriaMetrics components: consistently return 200 http status code from [`/-/reload` endpoint](https://docs.victoriametrics.com/vmagent/#configuration-update). Previously [single-node VictoriaMetrics](https://docs.victoriametrics.com/) was returning 204 http status code. See [this feature request](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5774).
+* BUGFIX: prevent from possible `too big indexBlockSize` panic.
 * BUGFIX: [vmui](https://docs.victoriametrics.com/#vmui): fix the graph dragging for Firefox and Safari. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5764).
 * BUGFIX: [vmui](https://docs.victoriametrics.com/#vmui): fix handling invalid timezone. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5732).
 * BUGFIX: [vmui](https://docs.victoriametrics.com/#vmui): fix the bug where the select does not open. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5728).
diff --git a/lib/mergeset/metaindex_row.go b/lib/mergeset/metaindex_row.go
index c06a4a1948..e80ba19a4f 100644
--- a/lib/mergeset/metaindex_row.go
+++ b/lib/mergeset/metaindex_row.go
@@ -72,8 +72,11 @@ func (mr *metaindexRow) Unmarshal(src []byte) ([]byte, error) {
 	if mr.blockHeadersCount <= 0 {
 		return src, fmt.Errorf("blockHeadersCount must be bigger than 0; got %d", mr.blockHeadersCount)
 	}
-	if mr.indexBlockSize > 2*maxIndexBlockSize {
-		return src, fmt.Errorf("too big indexBlockSize: %d; cannot exceed %d", mr.indexBlockSize, 2*maxIndexBlockSize)
+	if mr.indexBlockSize > 4*maxIndexBlockSize {
+		// The index block size can exceed maxIndexBlockSize by up to 4x,
+		// since it can contain commonPrefix and firstItem at blockHeader
+		// with the maximum length of maxIndexBlockSize per each field.
+		return src, fmt.Errorf("too big indexBlockSize: %d; cannot exceed %d", mr.indexBlockSize, 4*maxIndexBlockSize)
 	}
 
 	return src, nil