diff --git a/src/corelib/mimetypes/qmimeprovider.cpp b/src/corelib/mimetypes/qmimeprovider.cpp
index df1d68a764..9013cdf161 100644
--- a/src/corelib/mimetypes/qmimeprovider.cpp
+++ b/src/corelib/mimetypes/qmimeprovider.cpp
@@ -212,13 +212,13 @@ void QMimeBinaryProvider::addFileNameMatches(const QString &fileName, QMimeGlobM
     if (fileName.isEmpty())
         return;
     Q_ASSERT(m_cacheFile);
-    const QString lowerFileName = fileName.toLower();
     int numMatches = 0;
     // Check literals (e.g. "Makefile")
     numMatches = matchGlobList(result, m_cacheFile.get(),
                                m_cacheFile->getUint32(PosLiteralListOffset), fileName);
     // Check the very common *.txt cases with the suffix tree
     if (numMatches == 0) {
+        const QString lowerFileName = fileName.toLower();
         const int reverseSuffixTreeOffset = m_cacheFile->getUint32(PosReverseSuffixTreeOffset);
         const int numRoots = m_cacheFile->getUint32(reverseSuffixTreeOffset);
         const int firstRootOffset = m_cacheFile->getUint32(reverseSuffixTreeOffset + 4);