diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index d81bf40c7..65c8dc210 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -1,6 +1,7 @@
 #include "globals.hh"
 #include "misc.hh"
 #include "local-store.hh"
+#include "immutable.hh"
 
 #include <boost/shared_ptr.hpp>
 
@@ -396,11 +397,11 @@ struct LocalStore::GCState
     PathSet deleted;
     PathSet live;
     PathSet busy;
+    PathSet invalidated;
     bool gcKeepOutputs;
     bool gcKeepDerivations;
-    GCState(GCResults & results_) : results(results_)
-    {
-    }
+    unsigned long long bytesInvalidated;
+    GCState(GCResults & results_) : results(results_), bytesInvalidated(0) { }
 };
 
 
@@ -419,6 +420,16 @@ bool LocalStore::isActiveTempFile(const GCState & state,
 }
 
 
+void LocalStore::deleteGarbage(GCState & state, const Path & path)
+{
+    printMsg(lvlInfo, format("deleting `%1%'") % path);
+    unsigned long long bytesFreed, blocksFreed;
+    deletePathWrapped(path, bytesFreed, blocksFreed);
+    state.results.bytesFreed += bytesFreed;
+    state.results.blocksFreed += blocksFreed;
+}
+
+
 bool LocalStore::tryToDelete(GCState & state, const Path & path)
 {
     checkInterrupt();
@@ -502,15 +513,27 @@ bool LocalStore::tryToDelete(GCState & state, const Path & path)
 
     /* The path is garbage, so delete it. */
     if (shouldDelete(state.options.action)) {
-        printMsg(lvlInfo, format("deleting `%1%'") % path);
 
-        unsigned long long bytesFreed, blocksFreed;
-        deleteFromStore(path, bytesFreed, blocksFreed);
-        state.results.bytesFreed += bytesFreed;
-        state.results.blocksFreed += blocksFreed;
+        if (isValidPath(path)) {
+            /* If it's a valid path, invalidate it, rename it, and
+               schedule it for deletion.  The renaming is to ensure
+               that later (when we're not holding the global GC lock)
+               we can delete the path without being afraid that the
+               path has become alive again. */
+            printMsg(lvlInfo, format("invalidating `%1%'") % path);
+            // Estimate the amount freed using the narSize field.
+            state.bytesInvalidated += queryPathInfo(path).narSize;
+            invalidatePathChecked(path);
+            Path tmp = (format("%1%-gc-%2%") % path % getpid()).str();
+            makeMutable(path.c_str());
+            if (rename(path.c_str(), tmp.c_str()))
+                throw SysError(format("unable to rename `%1%' to `%2%'") % path % tmp);
+            state.invalidated.insert(tmp);
+        } else
+            deleteGarbage(state, path);
 
-        if (state.options.maxFreed && state.results.bytesFreed > state.options.maxFreed) {
-            printMsg(lvlInfo, format("deleted more than %1% bytes; stopping") % state.options.maxFreed);
+        if (state.options.maxFreed && state.results.bytesFreed + state.bytesInvalidated > state.options.maxFreed) {
+            printMsg(lvlInfo, format("deleted or invalidated more than %1% bytes; stopping") % state.options.maxFreed);
             throw GCLimitReached();
         }
 
@@ -635,6 +658,14 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
         } catch (GCLimitReached & e) {
         }
     }
+
+    /* Allow other processes to add to the store from here on. */
+    fdGCLock.close();
+
+    /* Delete the invalidated paths now that the lock has been
+       released. */
+    foreach (PathSet::iterator, i, state.invalidated)
+        deleteGarbage(state, *i);
 }
 
 
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index f3b779dd0..1ab9d15eb 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -1380,11 +1380,8 @@ Paths LocalStore::importPaths(bool requireSignature, Source & source)
 }
 
 
-void LocalStore::deleteFromStore(const Path & path, unsigned long long & bytesFreed,
-    unsigned long long & blocksFreed)
+void LocalStore::invalidatePathChecked(const Path & path)
 {
-    bytesFreed = 0;
-
     assertStorePath(path);
 
     while (1) {
@@ -1404,8 +1401,6 @@ void LocalStore::deleteFromStore(const Path & path, unsigned long long & bytesFr
             break;
         } catch (SQLiteBusy & e) { };
     }
-    
-    deletePathWrapped(path, bytesFreed, blocksFreed);
 }
 
 
diff --git a/src/libstore/local-store.hh b/src/libstore/local-store.hh
index 2739c4eea..8e3cbe5ce 100644
--- a/src/libstore/local-store.hh
+++ b/src/libstore/local-store.hh
@@ -164,10 +164,6 @@ public:
 
     void collectGarbage(const GCOptions & options, GCResults & results);
 
-    /* Delete a path from the Nix store. */
-    void deleteFromStore(const Path & path, unsigned long long & bytesFreed,
-        unsigned long long & blocksFreed);
-    
     /* Optimise the disk space usage of the Nix store by hard-linking
        files with the same contents. */
     void optimiseStore(bool dryRun, OptimiseStats & stats);
@@ -238,6 +234,9 @@ private:
 
     void invalidatePath(const Path & path);
 
+    /* Delete a path from the Nix store. */
+    void invalidatePathChecked(const Path & path);
+    
     void verifyPath(const Path & path, const PathSet & store,
         PathSet & done, PathSet & validPaths);
 
@@ -249,6 +248,8 @@ private:
 
     struct GCState;
 
+    void deleteGarbage(GCState & state, const Path & path);
+    
     bool tryToDelete(GCState & state, const Path & path);
     
     bool isActiveTempFile(const GCState & state,