diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 55637dd859..03c5d76b37 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -1229,6 +1229,8 @@ void LocalStore::upgradeStore6()
     
     if (sqlite3_exec(db, "begin;", 0, 0, 0) != SQLITE_OK)
         throw SQLiteError(db, "running `begin' command");
+
+    std::map<Path, sqlite3_int64> pathToId;
     
     foreach (PathSet::iterator, i, validPaths) {
         ValidPathInfo info = queryPathInfo(*i, true);
@@ -1245,12 +1247,24 @@ void LocalStore::upgradeStore6()
         if (sqlite3_step(registerStmt) != SQLITE_DONE)
             throw SQLiteError(db, "registering valid path in database");
 
+        pathToId[*i] = sqlite3_last_insert_rowid(db);
+
+        std::cerr << ".";
+    }
+
+    std::cerr << "|";
+    
+    foreach (PathSet::iterator, i, validPaths) {
+        ValidPathInfo info = queryPathInfo(*i, true);
+        
         foreach (PathSet::iterator, j, info.references) {
             if (sqlite3_reset(addRefStmt) != SQLITE_OK)
                 throw SQLiteError(db, "resetting statement");
-            if (sqlite3_bind_text(addRefStmt, 1, i->c_str(), -1, SQLITE_TRANSIENT) != SQLITE_OK)
+            if (sqlite3_bind_int(addRefStmt, 1, pathToId[*i]) != SQLITE_OK)
                 throw SQLiteError(db, "binding argument 1");
-            if (sqlite3_bind_text(addRefStmt, 2, j->c_str(), -1, SQLITE_TRANSIENT) != SQLITE_OK)
+            if (pathToId.find(*j) == pathToId.end())
+                throw Error(format("path `%1%' referenced by `%2%' is invalid") % *j % *i);
+            if (sqlite3_bind_int(addRefStmt, 2, pathToId[*j]) != SQLITE_OK)
                 throw SQLiteError(db, "binding argument 2");
             if (sqlite3_step(addRefStmt) != SQLITE_DONE)
                 throw SQLiteError(db, "adding reference to database");
diff --git a/src/libstore/schema.sql b/src/libstore/schema.sql
index e241329430..3c07978fc9 100644
--- a/src/libstore/schema.sql
+++ b/src/libstore/schema.sql
@@ -1,27 +1,24 @@
 pragma foreign_keys = on;
 
 create table if not exists ValidPaths (
-    path             text primary key not null,
+    id               integer primary key autoincrement not null,
+    path             text unique not null,
     hash             text not null,
     registrationTime integer not null
 );
 
 create table if not exists Refs (
-    referrer  text not null,
-    reference text not null,
+    referrer  integer not null,
+    reference integer not null,
     primary key (referrer, reference),
-    foreign key (referrer) references ValidPaths(path)
-      on delete cascade
-      deferrable initially deferred,
-    foreign key (reference) references ValidPaths(path)
-      on delete restrict
-      deferrable initially deferred
+    foreign key (referrer) references ValidPaths(id) on delete cascade,
+    foreign key (reference) references ValidPaths(id) on delete restrict
 );
 
+create index if not exists IndexReferrer on Refs(referrer);
+create index if not exists IndexReference on Refs(reference);
+
 create table if not exists FailedDerivations (
     path text primary key not null,
     time integer not null
 );
-
-create index IndexReferrer on Refs(referrer);
-create index IndexReference on Refs(reference);