diff --git a/scripts/nix-prefetch-url.in b/scripts/nix-prefetch-url.in
index 409c3f992d..b33aa8a850 100644
--- a/scripts/nix-prefetch-url.in
+++ b/scripts/nix-prefetch-url.in
@@ -25,7 +25,7 @@ if test -z "$hash"; then
         tmpPath1=/tmp/nix-prefetch-url-$$ # !!! security?
     fi
 
-    # Perform the checkout.
+    # Perform the download.
     @curl@ --fail --location --max-redirs 20 "$url" > $tmpPath1
 
     # Compute the hash.
@@ -47,7 +47,7 @@ storeExpr=$( \
     | @bindir@/nix-instantiate -)
 
 # Realise it.
-finalPath=$(@bindir@/nix-store -q --force-realise $storeExpr)
+finalPath=$(@bindir@/nix-store -r $storeExpr)
     
 if ! test -n "$QUIET"; then echo "path is $finalPath" >&2; fi
 
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index da9d1e6358..a2f27b4dc8 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -194,6 +194,7 @@ static Expr primDerivation(EvalState & state, const ATermVector & _args)
     
     string outputHash;
     string outputHashAlgo;
+    bool outputHashRecursive = false;
 
     for (ATermIterator i(attrs.keys()); i; ++i) {
         string key = aterm2String(*i);
@@ -228,6 +229,11 @@ static Expr primDerivation(EvalState & state, const ATermVector & _args)
             else if (key == "name") drvName = s;
             else if (key == "outputHash") outputHash = s;
             else if (key == "outputHashAlgo") outputHashAlgo = s;
+            else if (key == "outputHashMode") {
+                if (s == "recursive") outputHashRecursive = true; 
+                else if (s == "flat") outputHashRecursive = false;
+                else throw Error(format("invalid value `%1%' for `outputHashMode' attribute") % s);
+            }
         }
     }
     
@@ -255,6 +261,7 @@ static Expr primDerivation(EvalState & state, const ATermVector & _args)
             h = parseHash32(ht, outputHash);
         string s = outputHash;
         outputHash = printHash(h);
+        if (outputHashRecursive) outputHashAlgo = "r:" + outputHashAlgo;
     }
 
     /* Check the derivation name.  It shouldn't contain whitespace,
diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 1ba521eb37..f6b081aafc 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -1082,25 +1082,37 @@ void DerivationGoal::computeClosure()
            outputs (i.e., the content hash should match the specified
            hash). */ 
         if (i->second.hash != "") {
-            HashType ht = parseHashType(i->second.hashAlgo);
+
+            bool recursive = false;
+            string algo = i->second.hashAlgo;
+            
+            if (string(algo, 0, 2) == "r:") {
+                recursive = true;
+                algo = string(algo, 2);
+            }
+
+            if (!recursive) {
+                /* The output path should be a regular file without
+                   execute permission. */
+                struct stat st;
+                if (lstat(path.c_str(), &st))
+                    throw SysError(format("getting attributes of path `%1%'") % path);
+                if (!S_ISREG(st.st_mode) || (st.st_mode & S_IXUSR) != 0)
+                    throw Error(
+                        format("output path `%1% should be a non-executable regular file")
+                        % path);
+            }
+
+            /* Check the hash. */
+            HashType ht = parseHashType(algo);
             if (ht == htUnknown)
-                throw Error(format("unknown hash algorithm `%1%'") % i->second.hashAlgo);
+                throw Error(format("unknown hash algorithm `%1%'") % algo);
             Hash h = parseHash(ht, i->second.hash);
-            Hash h2 = hashFile(ht, path);
+            Hash h2 = recursive ? hashPath(ht, path) : hashFile(ht, path);
             if (h != h2)
                 throw Error(
                     format("output path `%1% should have %2% hash `%3%', instead has `%4%'")
-                    % path % i->second.hashAlgo % printHash(h) % printHash(h2));
-
-            /* Also, the output path should be a regular file withouth
-               execute permission. */
-            struct stat st;
-            if (lstat(path.c_str(), &st))
-                throw SysError(format("getting attributes of path `%1%'") % path);
-            if (!S_ISREG(st.st_mode) || (st.st_mode & S_IXUSR) != 0)
-                throw Error(
-                    format("output path `%1% should be a non-executable regular file")
-                    % path);
+                    % path % algo % printHash(h) % printHash(h2));
         }
 
 	canonicalisePathMetaData(path);