diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 1d611ffba..47a905c81 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -1458,7 +1458,7 @@ void replaceValidPath(const Path & storePath, const Path tmpPath)
        tmpPath (the replacement), so we have to move it out of the
        way first.  We'd better not be interrupted here, because if
        we're repairing (say) Glibc, we end up with a broken system. */
-    Path oldPath = (format("%1%.old-%2%-%3%") % storePath % getpid() % rand()).str();
+    Path oldPath = (format("%1%.old-%2%-%3%") % storePath % getpid() % random()).str();
     if (pathExists(storePath))
         rename(storePath.c_str(), oldPath.c_str());
     if (rename(tmpPath.c_str(), storePath.c_str()) == -1)
diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index 943b16c28..ba49749d8 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -59,7 +59,7 @@ static void makeSymlink(const Path & link, const Path & target)
 
     /* Create the new symlink. */
     Path tempLink = (format("%1%.tmp-%2%-%3%")
-        % link % getpid() % rand()).str();
+        % link % getpid() % random()).str();
     createSymlink(target, tempLink);
 
     /* Atomically replace the old one. */
diff --git a/src/libstore/optimise-store.cc b/src/libstore/optimise-store.cc
index 891540ae4..7840167d7 100644
--- a/src/libstore/optimise-store.cc
+++ b/src/libstore/optimise-store.cc
@@ -213,7 +213,7 @@ void LocalStore::optimisePath_(Activity * act, OptimiseStats & stats,
     MakeReadOnly makeReadOnly(mustToggle ? dirOf(path) : "");
 
     Path tempLink = (format("%1%/.tmp-link-%2%-%3%")
-        % realStoreDir % getpid() % rand()).str();
+        % realStoreDir % getpid() % random()).str();
 
     if (link(linkPath.c_str(), tempLink.c_str()) == -1) {
         if (errno == EMLINK) {