diff --git a/tsdb/head_wal.go b/tsdb/head_wal.go
index 326efe6887..5ef1fa311b 100644
--- a/tsdb/head_wal.go
+++ b/tsdb/head_wal.go
@@ -236,6 +236,7 @@ Outer:
 			seriesPool.Put(v)
 		case []record.RefSample:
 			samples := v
+			minValidTime := h.minValidTime.Load()
 			// We split up the samples into chunks of 5000 samples or less.
 			// With O(300 * #cores) in-flight sample batches, large scrapes could otherwise
 			// cause thousands of very large in flight buffers occupying large amounts
@@ -249,6 +250,9 @@ Outer:
 					shards[i] = processors[i].reuseBuf()
 				}
 				for _, sam := range samples[:m] {
+					if sam.T < minValidTime {
+						continue // Before minValidTime: discard.
+					}
 					if r, ok := multiRef[sam.Ref]; ok {
 						sam.Ref = r
 					}
@@ -412,11 +416,9 @@ func (wp *walSubsetProcessor) reuseBuf() []record.RefSample {
 
 // processWALSamples adds the samples it receives to the head and passes
 // the buffer received to an output channel for reuse.
-// Samples before the minValidTime timestamp are discarded.
 func (wp *walSubsetProcessor) processWALSamples(h *Head, mmappedChunks map[chunks.HeadSeriesRef][]*mmappedChunk) (unknownRefs, mmapOverlappingChunks uint64) {
 	defer close(wp.output)
 
-	minValidTime := h.minValidTime.Load()
 	mint, maxt := int64(math.MaxInt64), int64(math.MinInt64)
 
 	for in := range wp.input {
@@ -429,9 +431,6 @@ func (wp *walSubsetProcessor) processWALSamples(h *Head, mmappedChunks map[chunk
 		}
 
 		for _, s := range in.samples {
-			if s.T < minValidTime {
-				continue
-			}
 			ms := h.series.getByID(s.Ref)
 			if ms == nil {
 				unknownRefs++