diff --git a/server/filesystem/compress.go b/server/filesystem/compress.go
index 65c8b62..0c2cd8f 100644
--- a/server/filesystem/compress.go
+++ b/server/filesystem/compress.go
@@ -95,7 +95,7 @@ func (fs *Filesystem) SpaceAvailableForDecompression(ctx context.Context, dir st
 	}
 	defer f.Close()
 
-	format, _, err := archives.Identify(ctx, filepath.Base(file), f)
+	format, _, err := identifyArchive(ctx, file, f)
 	if err != nil && !errors.Is(err, archives.NoMatch) {
 		return err
 	}
@@ -172,7 +172,7 @@ func (fs *Filesystem) DecompressFile(ctx context.Context, dir string, file strin
 	defer f.Close()
 
 	// Identify the type of archive we are dealing with.
-	format, input, err := archives.Identify(ctx, filepath.Base(file), f)
+	format, input, err := identifyArchive(ctx, file, f)
 	if err != nil {
 		if errors.Is(err, archives.NoMatch) {
 			return newFilesystemError(ErrCodeUnknownArchive, err)
@@ -188,6 +188,18 @@ func (fs *Filesystem) DecompressFile(ctx context.Context, dir string, file strin
 	})
 }
 
+// identifyArchive identifies the format of an archive by its contents, and only
+// falls back to its file name when the contents are not recognized. Matching on
+// the name first reads an archive with the wrong extension, such as a .tar.gz
+// renamed to .zip, as a zip inside a gzip stream, which cannot be extracted.
+func identifyArchive(ctx context.Context, file string, f ufs.File) (archives.Format, io.Reader, error) {
+	format, input, err := archives.Identify(ctx, "", f)
+	if errors.Is(err, archives.NoMatch) {
+		return archives.Identify(ctx, filepath.Base(file), f)
+	}
+	return format, input, err
+}
+
 // ExtractTransfer extracts the archive of a server that is being transferred to
 // this node into the server's directory. Every file is kept, including ones the
 // denylist would refuse, since they are the server's own files.
diff --git a/server/filesystem/decompress_test.go b/server/filesystem/decompress_test.go
index 885d4fe..55fd4cf 100644
--- a/server/filesystem/decompress_test.go
+++ b/server/filesystem/decompress_test.go
@@ -143,3 +143,30 @@ func TestDecompressZipSymlinkEntry(t *testing.T) {
 	require.NoError(t, err)
 	assert.Equal(t, "target.txt", target)
 }
+
+// An archive created by the compress endpoint and renamed to a different
+// extension is still read as the format it actually is.
+func TestDecompressRenamedArchive(t *testing.T) {
+	fs, rfs := NewFs()
+	t.Cleanup(func() { _ = os.RemoveAll(rfs.root) })
+
+	fs.SetDiskLimit(1 << 20)
+	require.NoError(t, fs.CreateDirectory("source", "/"))
+	require.NoError(t, rfs.CreateServerFileFromString("source/file.txt", "hello"))
+
+	st, err := fs.CompressFiles("/", []string{"source"})
+	require.NoError(t, err)
+	require.NoError(t, fs.Rename(st.Name(), "renamed.zip"))
+	require.NoError(t, os.RemoveAll(filepath.Join(rfs.root, "server", "source")))
+
+	// The formats matching an archive are tried in random order, so a single
+	// attempt can pass by chance.
+	for i := 0; i < 10; i++ {
+		require.NoError(t, fs.SpaceAvailableForDecompression(context.Background(), "/", "renamed.zip"))
+		require.NoError(t, fs.DecompressFile(context.Background(), "/", "renamed.zip"))
+	}
+
+	got, err := os.ReadFile(filepath.Join(rfs.root, "server", "source", "file.txt"))
+	require.NoError(t, err)
+	assert.Equal(t, "hello", string(got))
+}