diff --git a/go.mod b/go.mod
index 8cf8cf5..fea5801 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,3 @@
 module github.com/bartventer/httpcache
 
-go 1.24
+go 1.25
diff --git a/store/acceptance/acceptance.go b/store/acceptance/acceptance.go
index 21a4acf..2c2fdfc 100644
--- a/store/acceptance/acceptance.go
+++ b/store/acceptance/acceptance.go
@@ -18,6 +18,7 @@ package acceptance
 import (
 	"bytes"
 	"slices"
+	"strings"
 	"testing"
 
 	"github.com/bartventer/httpcache/internal/testutil"
@@ -126,7 +127,11 @@ func testKeys(t *testing.T, factory FactoryFunc) {
 	if !ok {
 		t.Skip("Cache implementation does not support key listing")
 	}
-	keys := []string{"foo", "bar", "baz"}
+	keys := []string{
+		"foo",
+		"bar",
+		"baz" + strings.Repeat("x", 255), // ensure long key handling
+	}
 	for _, key := range keys {
 		value := []byte("value for " + key)
 		testutil.RequireNoError(t, cache.Set(key, value), "Set failed for key "+key)
diff --git a/store/fscache/filenamer.go b/store/fscache/filenamer.go
new file mode 100644
index 0000000..0c7b577
--- /dev/null
+++ b/store/fscache/filenamer.go
@@ -0,0 +1,90 @@
+// Copyright (c) 2025 Bart Venter <bartventer@proton.me>
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package fscache
+
+import (
+	"encoding/base64"
+	"path/filepath"
+	"strings"
+)
+
+type (
+	fileNamer     interface{ FileName(key string) string }
+	fileNameKeyer interface {
+		KeyFromFileName(name string) (string, error)
+	}
+)
+
+type (
+	fileNamerFunc     func(key string) string
+	fileNameKeyerFunc func(name string) (string, error)
+)
+
+func (f fileNamerFunc) FileName(key string) string                      { return f(key) }
+func (f fileNameKeyerFunc) KeyFromFileName(name string) (string, error) { return f(name) }
+
+// fragmentSize is the maximum filename length per directory level.
+// 48 is chosen so that 5 fragments fit within 240 chars, well under common filesystem limits.
+const fragmentSize = 48
+
+// fragmentingFileNamer returns a fileNamer that fragments long keys into directory structures.
+// This helps avoid filesystem limits on filename lengths.
+func fragmentingFileNamer() fileNamer {
+	return fileNamerFunc(fragmentFileName)
+}
+
+func fragmentFileName(key string) string {
+	encoded := base64.RawURLEncoding.EncodeToString([]byte(key))
+	if len(encoded) <= 255 { // Common filesystem filename limit
+		return encoded
+	}
+
+	// Fragment the encoded string
+	var parts []string
+	for i := 0; i < len(encoded); i += fragmentSize {
+		end := min(i+fragmentSize, len(encoded))
+		parts = append(parts, encoded[i:end])
+	}
+	return filepath.Join(parts...)
+}
+
+func fragmentingFileNameKeyer() fileNameKeyer {
+	return fileNameKeyerFunc(fragmentedFileNameToKey)
+}
+
+var filepathSeparatorReplacer = strings.NewReplacer(
+	string(filepath.Separator),
+	"",
+)
+
+func fragmentedFileNameToKey(name string) (string, error) {
+	// Check if the name contains path separators (i.e., is fragmented)
+	if strings.ContainsRune(name, filepath.Separator) {
+		// Handle fragmented path
+		base64Str := filepathSeparatorReplacer.Replace(name)
+		decoded, err := base64.RawURLEncoding.DecodeString(base64Str)
+		if err != nil {
+			return "", err
+		}
+		return string(decoded), nil
+	}
+
+	// Handle plain base64
+	decoded, err := base64.RawURLEncoding.DecodeString(name)
+	if err != nil {
+		return "", err
+	}
+	return string(decoded), nil
+}
diff --git a/store/fscache/filenamer_test.go b/store/fscache/filenamer_test.go
new file mode 100644
index 0000000..6168b20
--- /dev/null
+++ b/store/fscache/filenamer_test.go
@@ -0,0 +1,109 @@
+// Copyright (c) 2025 Bart Venter <bartventer@proton.me>
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package fscache
+
+import (
+	"encoding/base64"
+	"fmt"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/bartventer/httpcache/internal/testutil"
+)
+
+func Example_fragmentFileName_short() {
+	url := "https://short.url/test"
+	path := fragmentFileName(url)
+	fmt.Println("Fragmented path:", path)
+	// Output:
+	// Fragmented path: aHR0cHM6Ly9zaG9ydC51cmwvdGVzdA
+}
+
+func Example_fragmentFileName_long() {
+	url := "https://example.com/" + strings.Repeat("a", 255)
+	path := fragmentFileName(url)
+	fmt.Println("Fragmented path:", path)
+	// Output:
+	// Fragmented path: aHR0cHM6Ly9leGFtcGxlLmNvbS9hYWFhYWFhYWFhYWFhYWFh/YWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFh/YWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFh/YWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFh/YWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFh/YWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFh/YWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFh/YWFhYWFhYWFhYWFhYWFhYWFhYWFhYWE
+}
+
+func Test_fragmentFileName_fragmentedFileNameToKey(t *testing.T) {
+	cases := []struct {
+		name      string
+		url       string
+		assertion func(tt *testing.T, encoded, decoded string)
+	}{
+		{
+			name: "Empty string",
+			url:  "",
+		},
+		{
+			name: "Short ASCII URL",
+			url:  "https://example.com/test?foo=bar",
+		},
+		{
+			name: "Long ASCII URL",
+			url:  "https://example.com/" + strings.Repeat("a", 1000),
+			assertion: func(tt *testing.T, encoded string, _ string) {
+				for frag := range strings.SplitSeq(encoded, string(filepath.Separator)) {
+					testutil.AssertTrue(
+						tt,
+						len(frag) <= fragmentSize,
+						"Fragment too long: got %d, want <= %d",
+						len(frag),
+						fragmentSize,
+					)
+				}
+			},
+		},
+		{
+			name: "Unicode URL",
+			url:  "https://例子.测试?emoji=🚀",
+		},
+		{
+			name: "URL with separators",
+			url:  "https://foo/bar/baz?x=y/z",
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			encoded := fragmentFileName(tc.url)
+			// Roundtrip test
+			decoded, err := fragmentedFileNameToKey(encoded)
+			testutil.RequireNoError(t, err)
+			testutil.AssertEqual(t, tc.url, decoded, "Roundtrip failed")
+			if tc.assertion != nil {
+				tc.assertion(t, encoded, decoded)
+			}
+		})
+	}
+}
+
+func Test_fragmentedFileNameToKey_InvalidBase64(t *testing.T) {
+	invalidPaths := []string{
+		"!!!notbase64",
+		"this/is/not/valid/base64/===",
+		"foo/bar/baz",
+	}
+	for _, path := range invalidPaths {
+		t.Run(path, func(t *testing.T) {
+			_, err := fragmentedFileNameToKey(path)
+			var cie base64.CorruptInputError
+			testutil.RequireErrorAs(t, err, &cie)
+		})
+	}
+}
diff --git a/store/fscache/fscache.go b/store/fscache/fscache.go
index 079aa43..8dc86ba 100644
--- a/store/fscache/fscache.go
+++ b/store/fscache/fscache.go
@@ -49,16 +49,17 @@ import (
 	"cmp"
 	"context"
 	"crypto/rand"
-	"encoding/base64"
+	"io/fs"
+	"strings"
+
 	"errors"
 	"fmt"
 	"io"
-	"io/fs"
+
 	"net/url"
 	"os"
 	"path/filepath"
 	"slices"
-	"strings"
 	"time"
 
 	"github.com/bartventer/httpcache/store"
@@ -110,7 +111,7 @@ type fsCache struct {
 	// internal components
 
 	fn  fileNamer     // generates file names from keys
-	fnk fileNameKeyer // extracts keys from file names
+	fnk fileNameKeyer // recovers keys from file names
 	dw  dirWalker     // used for directory walking
 }
 
@@ -251,39 +252,22 @@ func (c *fsCache) initialize(appname string) error {
 	if err != nil {
 		return fmt.Errorf("fscache: could not open cache directory %q: %w", c.base, err)
 	}
-	c.fn = fileNamerFunc(safeFileName)
-	c.fnk = fileNameKeyerFunc(keyFromFileName)
+	c.fn = fragmentingFileNamer()
+	c.fnk = fragmentingFileNameKeyer()
 	c.dw = dirWalkerFunc(filepath.WalkDir)
 	c.timeout = cmp.Or(c.timeout, defaultTimeout)
 
 	return nil
 }
 
-type (
-	fileNamer     interface{ FileName(key string) string }
-	fileNameKeyer interface{ KeyFromFileName(name string) string }
-	dirWalker     interface {
-		WalkDir(root string, fn fs.WalkDirFunc) error
-	}
-)
+type dirWalker interface {
+	WalkDir(root string, fn fs.WalkDirFunc) error
+}
 
-type (
-	fileNamerFunc     func(key string) string
-	fileNameKeyerFunc func(name string) string
-	dirWalkerFunc     func(root string, fn fs.WalkDirFunc) error
-)
+type dirWalkerFunc func(root string, fn fs.WalkDirFunc) error
 
-func (f fileNamerFunc) FileName(key string) string                   { return f(key) }
-func (f fileNameKeyerFunc) KeyFromFileName(name string) string       { return f(name) }
 func (f dirWalkerFunc) WalkDir(root string, fn fs.WalkDirFunc) error { return f(root, fn) }
 
-func safeFileName(key string) string { return base64.RawURLEncoding.EncodeToString([]byte(key)) }
-
-func keyFromFileName(name string) string {
-	data, _ := base64.RawURLEncoding.DecodeString(name)
-	return string(data)
-}
-
 var _ driver.Conn = (*fsCache)(nil)
 var _ expapi.KeyLister = (*fsCache)(nil)
 
@@ -366,7 +350,11 @@ func (c *fsCache) set(key string, entry []byte) error {
 			return err
 		}
 	}
-	f, err := c.root.Create(c.fn.FileName(key))
+	name := c.fn.FileName(key)
+	if err := c.root.MkdirAll(filepath.Dir(name), 0o755); err != nil {
+		return err
+	}
+	f, err := c.root.Create(name)
 	if err != nil {
 		return err
 	}
@@ -448,7 +436,13 @@ func (c *fsCache) keys(prefix string) ([]string, error) {
 		if d.IsDir() {
 			return nil
 		}
-		if key := c.fnk.KeyFromFileName(filepath.Base(path)); strings.HasPrefix(key, prefix) {
+		key, err := c.fnk.KeyFromFileName(
+			strings.TrimPrefix(path, dirname+string(os.PathSeparator)),
+		)
+		if err != nil {
+			return err
+		}
+		if strings.HasPrefix(key, prefix) {
 			keys = append(keys, key)
 		}
 		return nil
diff --git a/store/fscache/fscache_test.go b/store/fscache/fscache_test.go
index 88068a6..f9ecd15 100644
--- a/store/fscache/fscache_test.go
+++ b/store/fscache/fscache_test.go
@@ -71,8 +71,8 @@ func Test_fsCache_KeysError(t *testing.T) {
 	cache.fn = fileNamerFunc(func(key string) string {
 		return key
 	})
-	cache.fnk = fileNameKeyerFunc(func(name string) string {
-		return name
+	cache.fnk = fileNameKeyerFunc(func(name string) (string, error) {
+		return name, nil
 	})
 	cache.dw = dirWalkerFunc(func(root string, fn fs.WalkDirFunc) error {
 		return testutil.ErrSample