diff --git a/CHANGELOG.md b/CHANGELOG.md
index a1ea3d9713..0bbf1c31a5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,7 @@ We use *breaking* word for marking changes that are not backward compatible (rel
 ### Fixed
 
 - [#2411](https://github.com/thanos-io/thanos/pull/2411) Query: fix a bug where queries might not time out sometimes due to issues with one or more StoreAPIs
+- [#2474](https://github.com/thanos-io/thanos/pull/2474) Store: fix a panic caused by concurrent memory access during block filtering.
 
 ## [v0.12.0](https://github.com/thanos-io/thanos/releases/tag/v0.12.0) - 2020.04.15
 
diff --git a/pkg/block/fetcher.go b/pkg/block/fetcher.go
index 7f21d4d801..29d67735e2 100644
--- a/pkg/block/fetcher.go
+++ b/pkg/block/fetcher.go
@@ -550,6 +550,7 @@ var _ MetadataFilter = &DeduplicateFilter{}
 // Not go-routine safe.
 type DeduplicateFilter struct {
 	duplicateIDs []ulid.ULID
+	mu           sync.Mutex
 }
 
 // NewDeduplicateFilter creates DeduplicateFilter.
@@ -603,11 +604,13 @@ func (f *DeduplicateFilter) filterForResolution(root *Node, metaSlice []*metadat
 
 	duplicateULIDs := getNonRootIDs(root)
 	for _, id := range duplicateULIDs {
+		f.mu.Lock()
 		if metas[id] != nil {
 			f.duplicateIDs = append(f.duplicateIDs, id)
 		}
 		synced.WithLabelValues(duplicateMeta).Inc()
 		delete(metas, id)
+		f.mu.Unlock()
 	}
 }