diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 95e6a3291..cfbf23ac4 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -957,39 +957,6 @@ std::exception_ptr RemoteStore::Connection::processStderr(Sink * sink, Source *
     return nullptr;
 }
 
-
-struct FramedSink : nix::BufferedSink
-{
-    ConnectionHandle & conn;
-    std::exception_ptr & ex;
-
-    FramedSink(ConnectionHandle & conn, std::exception_ptr & ex) : conn(conn), ex(ex)
-    { }
-
-    ~FramedSink()
-    {
-        try {
-            conn->to << 0;
-            conn->to.flush();
-        } catch (...) {
-            ignoreException();
-        }
-    }
-
-    void write(const unsigned char * data, size_t len) override
-    {
-        /* Don't send more data if the remote has
-            encountered an error. */
-        if (ex) {
-            auto ex2 = ex;
-            ex = nullptr;
-            std::rethrow_exception(ex2);
-        }
-        conn->to << len;
-        conn->to(data, len);
-    };
-};
-
 void
 ConnectionHandle::withFramedSink(std::function<void(Sink &sink)> fun) {
     (*this)->to.flush();
@@ -1022,7 +989,7 @@ ConnectionHandle::withFramedSink(std::function<void(Sink &sink)> fun) {
     });
 
     {
-        FramedSink sink(*this, ex);
+        FramedSink sink((*this)->to, ex);
         fun(sink);
         sink.flush();
     }
diff --git a/src/libutil/serialise.hh b/src/libutil/serialise.hh
index 6027d5961..3511e4cd8 100644
--- a/src/libutil/serialise.hh
+++ b/src/libutil/serialise.hh
@@ -406,8 +406,13 @@ struct StreamToSourceAdapter : Source
 };
 
 
-/* Like SizedSource, but guarantees that the whole frame is consumed after
-   destruction. This ensures that the original stream is in a known state. */
+/* A source that reads a distinct format of concatenated chunks back into its
+   logical form, in order to guarantee a known state to the original stream,
+   even in the event of errors.
+
+   Use with FramedSink, which also allows the logical stream to be terminated
+   in the event of an exception.
+*/
 struct FramedSource : Source
 {
     Source & from;
@@ -452,5 +457,42 @@ struct FramedSource : Source
     }
 };
 
+/* Write as chunks in the format expected by FramedSource.
+
+   The exception_ptr reference can be used to terminate the stream when you
+   detect that an error has occurred on the remote end.
+*/
+struct FramedSink : nix::BufferedSink
+{
+    BufferedSink & to;
+    std::exception_ptr & ex;
+
+    FramedSink(BufferedSink & to, std::exception_ptr & ex) : to(to), ex(ex)
+    { }
+
+    ~FramedSink()
+    {
+        try {
+            to << 0;
+            to.flush();
+        } catch (...) {
+            ignoreException();
+        }
+    }
+
+    void write(const unsigned char * data, size_t len) override
+    {
+        /* Don't send more data if the remote has
+            encountered an error. */
+        if (ex) {
+            auto ex2 = ex;
+            ex = nullptr;
+            std::rethrow_exception(ex2);
+        }
+        to << len;
+        to(data, len);
+    };
+};
+
 
 }