diff --git a/tools/disk_cache/api.go b/tools/disk_cache/api.go
index 37faabf7a..33adc4594 100644
--- a/tools/disk_cache/api.go
+++ b/tools/disk_cache/api.go
@@ -43,7 +43,9 @@ func NewDiskCache(path string, max_size int64) (dc *DiskCache, err error) {
 	if err = os.MkdirAll(path, 0o700); err != nil {
 		return
 	}
-	return &DiskCache{Path: path, MaxSize: max_size}, nil
+	dc = &DiskCache{Path: path, MaxSize: max_size}
+	err = dc.prune()
+	return
 }
 
 func KeyForPath(path string) (key string, err error) {
diff --git a/tools/disk_cache/implementation.go b/tools/disk_cache/implementation.go
index fd8eecb65..e989839d3 100644
--- a/tools/disk_cache/implementation.go
+++ b/tools/disk_cache/implementation.go
@@ -165,7 +165,7 @@ func (dc *DiskCache) remove(key string) (err error) {
 }
 
 func (dc *DiskCache) prune() error {
-	if dc.entries.TotalSize <= dc.MaxSize {
+	if dc.MaxSize < 1 || dc.entries.TotalSize <= dc.MaxSize {
 		return nil
 	}
 	for dc.entries.TotalSize > dc.MaxSize && len(dc.entries.SortedEntries) > 0 {
@@ -191,22 +191,26 @@ func (dc *DiskCache) update_timestamp(key string) {
 }
 
 func (dc *DiskCache) update_accounting(key string, changed int64) (err error) {
-	if err = dc.ensure_entries(); err == nil {
-		t := dc.entry_map[key]
-		if t == nil {
-			t = &Entry{Key: key}
-			dc.entry_map[key] = t
-			dc.entries.SortedEntries = append(dc.entries.SortedEntries, t)
-		}
-		old_size := t.Size
-		t.Size += changed
-		t.Size = max(0, t.Size)
-		dc.entries.TotalSize += t.Size - old_size
-		dc.update_timestamp(key)
-		dc.prune()
-		return dc.write_entries()
+	t := dc.entry_map[key]
+	if t == nil {
+		t = &Entry{Key: key}
+		dc.entry_map[key] = t
+		dc.entries.SortedEntries = append(dc.entries.SortedEntries, t)
 	}
-	return
+	old_size := t.Size
+	t.Size += changed
+	t.Size = max(0, t.Size)
+	dc.entries.TotalSize += t.Size - old_size
+	dc.update_timestamp(key)
+	dc.prune()
+	return dc.write_entries()
+}
+
+func (dc *DiskCache) keys() (ans []string, err error) {
+	if err = dc.ensure_entries(); err != nil {
+		return
+	}
+	return utils.Keys(dc.entry_map), nil
 }
 
 func (dc *DiskCache) add(key string, items map[string][]byte) (err error) {
diff --git a/tools/disk_cache/implementation_test.go b/tools/disk_cache/implementation_test.go
index ba2a68d2a..cf9ea5131 100644
--- a/tools/disk_cache/implementation_test.go
+++ b/tools/disk_cache/implementation_test.go
@@ -3,6 +3,8 @@ package disk_cache
 import (
 	"fmt"
 	"os"
+	"slices"
+	"strings"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
@@ -17,6 +19,11 @@ func TestDiskCache(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
+	dc2, err := NewDiskCache(tdir, dc.MaxSize)
+	if err != nil {
+		t.Fatal(err)
+	}
+
 	m := dc.Get("missing", "one", "two")
 	if diff := cmp.Diff(m, make(map[string]string)); diff != "" {
 		t.Fatalf("Unexpected return from missing: %s", diff)
@@ -24,18 +31,42 @@ func TestDiskCache(t *testing.T) {
 	dc.Add("k1", map[string][]byte{"1": []byte("abcd"), "2": []byte("efgh")})
 
 	ad := func(key string, expected map[string]string) {
-		actual := dc.Get(key, utils.Keys(expected)...)
+		for _, x := range []*DiskCache{dc, dc2} {
+			actual := x.Get(key, utils.Keys(expected)...)
 
-		for k, path := range actual {
-			d, err := os.ReadFile(path)
+			for k, path := range actual {
+				d, err := os.ReadFile(path)
+				if err != nil {
+					t.Fatal(err)
+				}
+				actual[k] = string(d)
+			}
+			if diff := cmp.Diff(expected, actual); diff != "" {
+				t.Fatalf("Data for %s not equal: %s", key, diff)
+			}
+		}
+	}
+	ak := func(keys ...string) {
+		for _, x := range []*DiskCache{dc, dc2} {
+			kk, err := x.keys()
 			if err != nil {
 				t.Fatal(err)
 			}
-			actual[k] = string(d)
-		}
-		if diff := cmp.Diff(expected, actual); diff != "" {
-			t.Fatalf("Data for %s not equal: %s", key, diff)
+			slices.Sort(kk)
+			slices.Sort(keys)
+			if diff := cmp.Diff(keys, kk); diff != "" {
+				t.Fatalf("Unexpected keys: %s", diff)
+			}
 		}
 	}
 	ad("k1", map[string]string{"1": "abcd", "2": "efgh"})
+	dc.Add("k1", map[string][]byte{"3": []byte("ijk"), "4": []byte("lmo")})
+	dc2.Add("k2", map[string][]byte{"1": []byte("123456789")})
+	ad("k1", map[string]string{"1": "abcd", "2": "efgh", "3": "ijk"})
+	if dc.entries.TotalSize != 14+9 {
+		t.Fatalf("TotalSize: %d != %d", dc.entries.TotalSize, 14+9)
+	}
+	ak("k1", "k2")
+	dc.Add("k3", map[string][]byte{"1": []byte(strings.Repeat("a", int(dc.MaxSize)-10))})
+	ak("k3", "k2")
 }