diff --git a/internal/delivery/target_database_export_test.go b/internal/delivery/target_database_export_test.go
index 6515b7d..fc6dd61 100644
--- a/internal/delivery/target_database_export_test.go
+++ b/internal/delivery/target_database_export_test.go
@@ -460,8 +460,13 @@ func TestArchiveExport_OneFileOpenAtATime(t *testing.T) {
 }
 
 // heapPeak is an io.Writer that discards what it is given and records
-// the largest heap it saw at a write. It collects garbage before each
-// reading, so the heap it reads is what is still held.
+// the largest heap it saw at a write. It collects garbage twice before
+// each reading, so the heap it reads is what is still held. Once is not
+// enough: the libraries the export calls (regexp, under GORM's table
+// names, and encoding/json among them) cache buffers in a sync.Pool,
+// which keeps them through one collection, so after one the reading
+// counts however many happen to be cached. That varies from run to run
+// by about as much as the limit in TestArchiveExport_Streams.
 type heapPeak struct {
 	max uint64
 }
@@ -469,6 +474,7 @@ type heapPeak struct {
 func (p *heapPeak) Write(b []byte) (int, error) {
 	var m runtime.MemStats
 
+	runtime.GC()
 	runtime.GC()
 	runtime.ReadMemStats(&m)
 	p.max = max(p.max, m.HeapAlloc)
@@ -498,6 +504,8 @@ func exportHeapGrowth(t *testing.T, rows, bodySize int) uint64 {
 
 	export := listExport(t, path)
 
+	// Twice, for the reason heapPeak gives.
+	runtime.GC()
 	runtime.GC()
 
 	var start runtime.MemStats