diff --git a/src/corelib/time/qtimezoneprivate_tz.cpp b/src/corelib/time/qtimezoneprivate_tz.cpp
index e68a7d4726a..c682fc8f70d 100644
--- a/src/corelib/time/qtimezoneprivate_tz.cpp
+++ b/src/corelib/time/qtimezoneprivate_tz.cpp
@@ -20,6 +20,8 @@
 #include <qplatformdefs.h>
 
 #include <algorithm>
+#include <memory>
+
 #include <errno.h>
 #include <limits.h>
 #ifndef Q_OS_INTEGRITY
@@ -980,8 +982,16 @@ QTzTimeZoneCacheEntry QTzTimeZoneCache::fetchEntry(const QByteArray &ianaId)
         return *obj;
 
     // ... or build a new entry from scratch
+
+    locker.unlock(); // don't parse files under mutex lock
+
     QTzTimeZoneCacheEntry ret = findEntry(ianaId);
-    m_cache.insert(ianaId, new QTzTimeZoneCacheEntry(ret));
+    auto ptr = std::make_unique<QTzTimeZoneCacheEntry>(ret);
+
+    locker.relock();
+    m_cache.insert(ianaId, ptr.release()); // may overwrite if another thread was faster
+    locker.unlock();
+
     return ret;
 }