diff --git a/src/libstore/optimise-store.cc b/src/libstore/optimise-store.cc
index b736307b..5093305a 100644
--- a/src/libstore/optimise-store.cc
+++ b/src/libstore/optimise-store.cc
@@ -249,14 +249,24 @@ void LocalStore::optimisePath_(OptimiseStats & stats, const Path & path, InodeHa
 
 void LocalStore::optimiseStore(OptimiseStats & stats)
 {
+    Activity act(*logger, actOptimiseStore);
+
     PathSet paths = queryAllValidPaths();
     InodeHash inodeHash = loadInodeHash();
 
+    act.progress(0, paths.size());
+
+    uint64_t done = 0;
+
     for (auto & i : paths) {
         addTempRoot(i);
         if (!isValidPath(i)) continue; /* path was GC'ed, probably */
-        //Activity act(*logger, lvlChatty, format("hashing files in '%1%'") % i);
-        optimisePath_(stats, realStoreDir + "/" + baseNameOf(i), inodeHash);
+        {
+            Activity act(*logger, actUnknown, fmt("optimising path '%s'", i));
+            optimisePath_(stats, realStoreDir + "/" + baseNameOf(i), inodeHash);
+        }
+        done++;
+        act.progress(done, paths.size());
     }
 }
 
diff --git a/src/libutil/logging.hh b/src/libutil/logging.hh
index edc3553f..bb89643d 100644
--- a/src/libutil/logging.hh
+++ b/src/libutil/logging.hh
@@ -21,6 +21,7 @@ typedef enum {
     actCopyPaths = 103,
     actBuilds = 104,
     actBuild = 105,
+    actOptimiseStore = 106,
 } ActivityType;
 
 typedef uint64_t ActivityId;
diff --git a/src/nix/optimise-store.cc b/src/nix/optimise-store.cc
new file mode 100644
index 00000000..725fb75a
--- /dev/null
+++ b/src/nix/optimise-store.cc
@@ -0,0 +1,41 @@
+#include "command.hh"
+#include "shared.hh"
+#include "store-api.hh"
+
+#include <atomic>
+
+using namespace nix;
+
+struct CmdOptimiseStore : StoreCommand
+{
+    CmdOptimiseStore()
+    {
+    }
+
+    std::string name() override
+    {
+        return "optimise-store";
+    }
+
+    std::string description() override
+    {
+        return "replace identical files in the store by hard links";
+    }
+
+    Examples examples() override
+    {
+        return {
+            Example{
+                "To optimise the Nix store:",
+                "nix optimise-store"
+            },
+        };
+    }
+
+    void run(ref<Store> store) override
+    {
+        store->optimiseStore();
+    }
+};
+
+static RegisterCommand r1(make_ref<CmdOptimiseStore>());
diff --git a/src/nix/progress-bar.cc b/src/nix/progress-bar.cc
index 62887370..15ef9537 100644
--- a/src/nix/progress-bar.cc
+++ b/src/nix/progress-bar.cc
@@ -210,7 +210,7 @@ public:
 
         std::string res;
 
-        auto renderActivity = [&](ActivityType type, const std::string & itemFmt, const std::string & numberFmt, double unit) {
+        auto renderActivity = [&](ActivityType type, const std::string & itemFmt, const std::string & numberFmt = "%d", double unit = 1) {
             auto & act = state.activitiesByType[type];
             uint64_t done = act.done, expected = act.done, running = 0, failed = act.failed;
             for (auto & j : act.its) {
@@ -242,16 +242,16 @@ public:
             return s;
         };
 
-        auto showActivity = [&](ActivityType type, const std::string & itemFmt, const std::string & numberFmt, double unit) {
+        auto showActivity = [&](ActivityType type, const std::string & itemFmt, const std::string & numberFmt = "%d", double unit = 1) {
             auto s = renderActivity(type, itemFmt, numberFmt, unit);
             if (s.empty()) return;
             if (!res.empty()) res += ", ";
             res += s;
         };
 
-        showActivity(actBuilds, "%s built", "%d", 1);
+        showActivity(actBuilds, "%s built");
 
-        auto s1 = renderActivity(actCopyPaths, "%s copied", "%d", 1);
+        auto s1 = renderActivity(actCopyPaths, "%s copied");
         auto s2 = renderActivity(actCopyPath, "%s MiB", "%.1f", MiB);
 
         if (!s1.empty() || !s2.empty()) {
@@ -262,6 +262,8 @@ public:
 
         showActivity(actDownload, "%s MiB DL", "%.1f", MiB);
 
+        showActivity(actOptimiseStore, "%s paths optimised");
+
         return res;
     }
 };