diff --git a/src/libmain/shared.cc b/src/libmain/shared.cc
index c83e997b2..f300fbf1b 100644
--- a/src/libmain/shared.cc
+++ b/src/libmain/shared.cc
@@ -342,4 +342,19 @@ RunPager::~RunPager()
 }
 
 
+string showBytes(unsigned long long bytes)
+{
+    return (format("%.2f MiB") % (bytes / (1024.0 * 1024.0))).str();
+}
+
+
+PrintFreed::~PrintFreed()
+{
+    if (show)
+        std::cout << format("%1% store paths deleted, %2% freed\n")
+            % results.paths.size()
+            % showBytes(results.bytesFreed);
+}
+
+
 }
diff --git a/src/libmain/shared.hh b/src/libmain/shared.hh
index b662c6cce..a7e6ef762 100644
--- a/src/libmain/shared.hh
+++ b/src/libmain/shared.hh
@@ -83,4 +83,21 @@ private:
 
 extern volatile ::sig_atomic_t blockInt;
 
+
+/* GC helpers. */
+
+string showBytes(unsigned long long bytes);
+
+class GCResults;
+
+struct PrintFreed
+{
+    bool show;
+    const GCResults & results;
+    PrintFreed(bool show, const GCResults & results)
+        : show(show), results(results) { }
+    ~PrintFreed();
+};
+
+
 }
diff --git a/src/nix-collect-garbage/nix-collect-garbage.cc b/src/nix-collect-garbage/nix-collect-garbage.cc
index a8f6c03c2..740ef88f5 100644
--- a/src/nix-collect-garbage/nix-collect-garbage.cc
+++ b/src/nix-collect-garbage/nix-collect-garbage.cc
@@ -1,3 +1,4 @@
+#include "store-api.hh"
 #include "hash.hh"
 #include "shared.hh"
 #include "globals.hh"
@@ -87,7 +88,13 @@ int main(int argc, char * * argv)
         if (removeOld) removeOldGenerations(profilesDir);
 
         // Run the actual garbage collector.
-        if (!dryRun) runProgramSimple(settings.nixBinDir + "/nix-store", Strings{"--gc"});
+        if (!dryRun) {
+            store = openStore(false);
+            GCOptions options;
+            options.action = GCOptions::gcDeleteDead;
+            GCResults results;
+            PrintFreed freed(true, results);
+            store->collectGarbage(options, results);
+        }
     });
 }
-
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index 506c1a397..ff15875e7 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -625,28 +625,6 @@ static void opCheckValidity(Strings opFlags, Strings opArgs)
 }
 
 
-static string showBytes(unsigned long long bytes)
-{
-    return (format("%.2f MiB") % (bytes / (1024.0 * 1024.0))).str();
-}
-
-
-struct PrintFreed
-{
-    bool show;
-    const GCResults & results;
-    PrintFreed(bool show, const GCResults & results)
-        : show(show), results(results) { }
-    ~PrintFreed()
-    {
-        if (show)
-            cout << format("%1% store paths deleted, %2% freed\n")
-                % results.paths.size()
-                % showBytes(results.bytesFreed);
-    }
-};
-
-
 static void opGC(Strings opFlags, Strings opArgs)
 {
     bool printRoots = false;