diff --git a/src/k7zip.cpp b/src/k7zip.cpp
--- a/src/k7zip.cpp
+++ b/src/k7zip.cpp
@@ -1676,6 +1676,7 @@
         }
 
         QByteArray inflated;
+        inflated.reserve(unpackSize);
         for (const QByteArray& data : qAsConst(inflatedDatas)) {
             inflated.append(data);
         }