diff --git a/src/libstore/daemon.cc b/src/libstore/daemon.cc
index 2eb566080..dc4889dfd 100644
--- a/src/libstore/daemon.cc
+++ b/src/libstore/daemon.cc
@@ -431,25 +431,30 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
                 hashAlgo = parseHashType(hashAlgoRaw);
             }
 
-            StringSink saved;
-            TeeSource savedNARSource(from, saved);
-            RetrieveRegularNARSink savedRegular { saved };
-
-            if (method == FileIngestionMethod::Recursive) {
-                /* Get the entire NAR dump from the client and save it to
-                  a string so that we can pass it to
-                  addToStoreFromDump(). */
-                ParseSink sink; /* null sink; just parse the NAR */
-                parseDump(sink, savedNARSource);
-            } else
-                parseDump(savedRegular, from);
-
+            auto dumpSource = sinkToSource([&](Sink & saved) {
+                if (method == FileIngestionMethod::Recursive) {
+                    /* We parse the NAR dump through into `saved` unmodified,
+                       so why all this extra work? We still parse the NAR so
+                       that we aren't sending arbitrary data to `saved`
+                       unwittingly`, and we know when the NAR ends so we don't
+                       consume the rest of `from` and can't parse another
+                       command. (We don't trust `addToStoreFromDump` to not
+                       eagerly consume the entire stream it's given, past the
+                       length of the Nar. */
+                    TeeSource savedNARSource(from, saved);
+                    ParseSink sink; /* null sink; just parse the NAR */
+                    parseDump(sink, savedNARSource);
+                } else {
+                    /* Incrementally parse the NAR file, stripping the
+                       metadata, and streaming the sole file we expect into
+                       `saved`. */
+                    RetrieveRegularNARSink savedRegular { saved };
+                    parseDump(savedRegular, from);
+                    if (!savedRegular.regular) throw Error("regular file expected");
+                }
+            });
             logger->startWork();
-            if (!savedRegular.regular) throw Error("regular file expected");
-
-            // FIXME: try to stream directly from `from`.
-            StringSource dumpSource { *saved.s };
-            auto path = store->addToStoreFromDump(dumpSource, baseName, method, hashAlgo);
+            auto path = store->addToStoreFromDump(*dumpSource, baseName, method, hashAlgo);
             logger->stopWork();
 
             to << store->printStorePath(path);
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 64019314f..3a1688272 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -8,6 +8,7 @@
 #include "references.hh"
 #include "callback.hh"
 #include "topo-sort.hh"
+#include "finally.hh"
 
 #include <iostream>
 #include <algorithm>
@@ -1333,13 +1334,15 @@ StorePath LocalStore::addToStoreFromDump(Source & source0, const string & name,
         auto want = std::min(chunkSize, settings.narBufferSize - oldSize);
         dump.resize(oldSize + want);
         auto got = 0;
+        Finally cleanup([&]() {
+            dump.resize(oldSize + got);
+        });
         try {
             got = source.read(dump.data() + oldSize, want);
         } catch (EndOfFile &) {
             inMemory = true;
             break;
         }
-        dump.resize(oldSize + got);
     }
 
     std::unique_ptr<AutoDelete> delTempDir;