diff --git a/src/libutil/fs-sink.cc b/src/libutil/fs-sink.cc
index fcffd3216..a08a723a4 100644
--- a/src/libutil/fs-sink.cc
+++ b/src/libutil/fs-sink.cc
@@ -15,68 +15,63 @@ static RestoreSinkSettings restoreSinkSettings;
 
 static GlobalConfig::Register r1(&restoreSinkSettings);
 
-struct RestoreSink : ParseSink
+
+void RestoreSink::createDirectory(const Path & path)
 {
-    Path dstPath;
-    AutoCloseFD fd;
-
-    void createDirectory(const Path & path) override
-    {
-        Path p = dstPath + path;
-        if (mkdir(p.c_str(), 0777) == -1)
-            throw SysError("creating directory '%1%'", p);
-    };
-
-    void createRegularFile(const Path & path) override
-    {
-        Path p = dstPath + path;
-        fd = open(p.c_str(), O_CREAT | O_EXCL | O_WRONLY | O_CLOEXEC, 0666);
-        if (!fd) throw SysError("creating file '%1%'", p);
-    }
-
-    void closeRegularFile() override
-    {
-        /* Call close explicitly to make sure the error is checked */
-        fd.close();
-    }
-
-    void isExecutable() override
-    {
-        struct stat st;
-        if (fstat(fd.get(), &st) == -1)
-            throw SysError("fstat");
-        if (fchmod(fd.get(), st.st_mode | (S_IXUSR | S_IXGRP | S_IXOTH)) == -1)
-            throw SysError("fchmod");
-    }
-
-    void preallocateContents(uint64_t len) override
-    {
-        if (!archiveSettings.preallocateContents)
-            return;
-
-#if HAVE_POSIX_FALLOCATE
-        if (len) {
-            errno = posix_fallocate(fd.get(), 0, len);
-            /* Note that EINVAL may indicate that the underlying
-               filesystem doesn't support preallocation (e.g. on
-               OpenSolaris).  Since preallocation is just an
-               optimisation, ignore it. */
-            if (errno && errno != EINVAL && errno != EOPNOTSUPP && errno != ENOSYS)
-                throw SysError("preallocating file of %1% bytes", len);
-        }
-#endif
-    }
-
-    void receiveContents(std::string_view data) override
-    {
-        writeFull(fd.get(), data);
-    }
-
-    void createSymlink(const Path & path, const std::string & target) override
-    {
-        Path p = dstPath + path;
-        nix::createSymlink(target, p);
-    }
+    Path p = dstPath + path;
+    if (mkdir(p.c_str(), 0777) == -1)
+        throw SysError("creating directory '%1%'", p);
 };
 
+void RestoreSink::createRegularFile(const Path & path)
+{
+    Path p = dstPath + path;
+    fd = open(p.c_str(), O_CREAT | O_EXCL | O_WRONLY | O_CLOEXEC, 0666);
+    if (!fd) throw SysError("creating file '%1%'", p);
+}
+
+void RestoreSink::closeRegularFile()
+{
+    /* Call close explicitly to make sure the error is checked */
+    fd.close();
+}
+
+void RestoreSink::isExecutable()
+{
+    struct stat st;
+    if (fstat(fd.get(), &st) == -1)
+        throw SysError("fstat");
+    if (fchmod(fd.get(), st.st_mode | (S_IXUSR | S_IXGRP | S_IXOTH)) == -1)
+        throw SysError("fchmod");
+}
+
+void RestoreSink::preallocateContents(uint64_t len)
+{
+    if (!restoreSinkSettings.preallocateContents)
+        return;
+
+#if HAVE_POSIX_FALLOCATE
+    if (len) {
+        errno = posix_fallocate(fd.get(), 0, len);
+        /* Note that EINVAL may indicate that the underlying
+           filesystem doesn't support preallocation (e.g. on
+           OpenSolaris).  Since preallocation is just an
+           optimisation, ignore it. */
+        if (errno && errno != EINVAL && errno != EOPNOTSUPP && errno != ENOSYS)
+            throw SysError("preallocating file of %1% bytes", len);
+    }
+#endif
+}
+
+void RestoreSink::receiveContents(std::string_view data)
+{
+    writeFull(fd.get(), data);
+}
+
+void RestoreSink::createSymlink(const Path & path, const std::string & target)
+{
+    Path p = dstPath + path;
+    nix::createSymlink(target, p);
+}
+
 }
diff --git a/src/libutil/fs-sink.hh b/src/libutil/fs-sink.hh
index ed6484e61..6837e2fc4 100644
--- a/src/libutil/fs-sink.hh
+++ b/src/libutil/fs-sink.hh
@@ -22,4 +22,21 @@ struct ParseSink
     virtual void createSymlink(const Path & path, const std::string & target) { };
 };
 
+struct RestoreSink : ParseSink
+{
+    Path dstPath;
+    AutoCloseFD fd;
+
+
+    void createDirectory(const Path & path) override;
+
+    void createRegularFile(const Path & path) override;
+    void closeRegularFile() override;
+    void isExecutable() override;
+    void preallocateContents(uint64_t size) override;
+    void receiveContents(std::string_view data) override;
+
+    void createSymlink(const Path & path, const std::string & target) override;
+};
+
 }