diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index b61ea5298..61286ceac 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -1249,8 +1249,7 @@ void DerivationGoal::inputsRealised()
         }
 
     /* Second, the input sources. */
-    for (auto & i : drv->inputSrcs)
-        worker.store.computeFSClosure(i, inputPaths);
+    worker.store.computeFSClosure(drv->inputSrcs, inputPaths);
 
     debug(format("added input paths %1%") % showPaths(inputPaths));
 
diff --git a/src/libstore/misc.cc b/src/libstore/misc.cc
index 0c2c49e55..9a88cdc31 100644
--- a/src/libstore/misc.cc
+++ b/src/libstore/misc.cc
@@ -8,7 +8,7 @@
 namespace nix {
 
 
-void Store::computeFSClosure(const Path & startPath,
+void Store::computeFSClosure(const PathSet & startPaths,
     PathSet & paths_, bool flipDirection, bool includeOutputs, bool includeDerivers)
 {
     struct State
@@ -85,7 +85,8 @@ void Store::computeFSClosure(const Path & startPath,
             });
     };
 
-    enqueue(startPath);
+    for (auto & startPath : startPaths)
+        enqueue(startPath);
 
     {
         auto state(state_.lock());
@@ -95,6 +96,13 @@ void Store::computeFSClosure(const Path & startPath,
 }
 
 
+void Store::computeFSClosure(const Path & startPath,
+    PathSet & paths_, bool flipDirection, bool includeOutputs, bool includeDerivers)
+{
+    computeFSClosure(PathSet{startPath}, paths_, flipDirection, includeOutputs, includeDerivers);
+}
+
+
 void Store::queryMissing(const PathSet & targets,
     PathSet & willBuild_, PathSet & willSubstitute_, PathSet & unknown_,
     unsigned long long & downloadSize_, unsigned long long & narSize_)
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index f6bbc9a84..2ea74d90e 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -477,15 +477,19 @@ public:
        ensurePath(). */
     Derivation derivationFromPath(const Path & drvPath);
 
-    /* Place in `paths' the set of all store paths in the file system
+    /* Place in `out' the set of all store paths in the file system
        closure of `storePath'; that is, all paths than can be directly
-       or indirectly reached from it.  `paths' is not cleared.  If
+       or indirectly reached from it.  `out' is not cleared.  If
        `flipDirection' is true, the set of paths that can reach
        `storePath' is returned; that is, the closures under the
        `referrers' relation instead of the `references' relation is
        returned. */
+    void computeFSClosure(const PathSet & paths,
+        PathSet & out, bool flipDirection = false,
+        bool includeOutputs = false, bool includeDerivers = false);
+
     void computeFSClosure(const Path & path,
-        PathSet & paths, bool flipDirection = false,
+        PathSet & out, bool flipDirection = false,
         bool includeOutputs = false, bool includeDerivers = false);
 
     /* Given a set of paths that are to be built, return the set of
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index a8cb46319..63e20a8c7 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -424,10 +424,9 @@ static void opQuery(Strings opFlags, Strings opArgs)
         case qRoots: {
             PathSet referrers;
             for (auto & i : opArgs) {
-                PathSet paths = maybeUseOutputs(store->followLinksToStorePath(i), useOutput, forceRealise);
-                for (auto & j : paths)
-                    store->computeFSClosure(j, referrers, true,
-                        settings.gcKeepOutputs, settings.gcKeepDerivations);
+                store->computeFSClosure(
+                    maybeUseOutputs(store->followLinksToStorePath(i), useOutput, forceRealise),
+                    referrers, true, settings.gcKeepOutputs, settings.gcKeepDerivations);
             }
             Roots roots = store->findRoots();
             for (auto & i : roots)
@@ -961,10 +960,9 @@ static void opServe(Strings opFlags, Strings opArgs)
 
             case cmdQueryClosure: {
                 bool includeOutputs = readInt(in);
-                PathSet paths = readStorePaths<PathSet>(*store, in);
                 PathSet closure;
-                for (auto & i : paths)
-                    store->computeFSClosure(i, closure, false, includeOutputs);
+                store->computeFSClosure(readStorePaths<PathSet>(*store, in),
+                    closure, false, includeOutputs);
                 out << closure;
                 break;
             }
diff --git a/src/nix/command.cc b/src/nix/command.cc
index fdf6ae6af..5a8288da9 100644
--- a/src/nix/command.cc
+++ b/src/nix/command.cc
@@ -106,8 +106,8 @@ void StorePathsCommand::run(ref<Store> store)
 
         if (recursive) {
             PathSet closure;
-            for (auto & storePath : storePaths)
-                store->computeFSClosure(storePath, closure, false, false);
+            store->computeFSClosure(PathSet(storePaths.begin(), storePaths.end()),
+                closure, false, false);
             storePaths = Paths(closure.begin(), closure.end());
         }
     }