diff --git a/src/libstore/store-dir-config.cc b/src/libstore/store-dir-config.cc
index 8c756ff5819..6d95ac09e8b 100644
--- a/src/libstore/store-dir-config.cc
+++ b/src/libstore/store-dir-config.cc
@@ -49,7 +49,13 @@ StorePathSet StoreDirConfig::parseStorePathSet(const PathSet & paths) const
 
 std::string StoreDirConfig::printStorePath(const StorePath & path) const
 {
-    return (storeDir + "/").append(path.to_string());
+    std::string res;
+    auto baseName = path.to_string();
+    res.reserve(storeDir.size() + 1 + baseName.size());
+    res.append(storeDir);
+    res.push_back('/');
+    res.append(baseName);
+    return res;
 }
 
 PathSet StoreDirConfig::printStorePathSet(const StorePathSet & paths) const