https://github.com/zealdocs/zeal/commit/11f6a85bb5f314ba8e1dbdc7654ef2647b75161e
Index: src/libs/ui/docsetsdialog.cpp
--- src/libs/ui/docsetsdialog.cpp.orig
+++ src/libs/ui/docsetsdialog.cpp
@@ -360,7 +360,8 @@ void DocsetsDialog::downloadCompleted()
         QTemporaryFile *tmpFile = m_tmpFiles[docsetName];
         if (!tmpFile) {
             tmpFile = new QTemporaryFile(QStringLiteral("%1/%2.XXXXXX.tmp").arg(Core::Application::cacheLocation(), docsetName), this);
-            tmpFile->open();
+            if (!tmpFile->open())
+                return;
             m_tmpFiles.insert(docsetName, tmpFile);
         }
 
@@ -403,7 +404,8 @@ void DocsetsDialog::downloadProgress(qint64 received, 
         QTemporaryFile *tmpFile = m_tmpFiles[docsetName];
         if (!tmpFile) {
             tmpFile = new QTemporaryFile(QStringLiteral("%1/%2.XXXXXX.tmp").arg(Core::Application::cacheLocation(), docsetName), this);
-            tmpFile->open();
+            if (!tmpFile->open())
+                return;
             m_tmpFiles.insert(docsetName, tmpFile);
         }
 
