diff --git a/src/corelib/io/qdataurl.cpp b/src/corelib/io/qdataurl.cpp
index 65b934b3f67..c5ecca8fb82 100644
--- a/src/corelib/io/qdataurl.cpp
+++ b/src/corelib/io/qdataurl.cpp
@@ -47,10 +47,10 @@ Q_CORE_EXPORT bool qDecodeDataUrl(const QUrl &uri, QString &mimeType, QByteArray
         QLatin1StringView textPlain;
         constexpr auto charset = "charset"_L1;
         if (QLatin1StringView{data}.startsWith(charset, Qt::CaseInsensitive)) {
-            qsizetype i = charset.size();
-            while (data.at(i) == ' ')
-                ++i;
-            if (data.at(i) == '=')
+            QByteArrayView copy = data.sliced(charset.size());
+            while (copy.startsWith(' '))
+                copy.slice(1);
+            if (copy.startsWith('='))
                 textPlain = "text/plain;"_L1;
         }
 
diff --git a/tests/auto/corelib/io/qdataurl/tst_qdataurl.cpp b/tests/auto/corelib/io/qdataurl/tst_qdataurl.cpp
index e694a791015..943b168e056 100644
--- a/tests/auto/corelib/io/qdataurl/tst_qdataurl.cpp
+++ b/tests/auto/corelib/io/qdataurl/tst_qdataurl.cpp
@@ -34,6 +34,8 @@ void tst_QDataUrl::decode_data()
         "text/plain"_L1, QByteArray::fromPercentEncoding("%E2%88%9A"));
     row("everythingIsCaseInsensitive", "Data:texT/PlaiN;charSet=iSo-8859-1;Base64,SGVsbG8=", true,
         "texT/PlaiN;charSet=iSo-8859-1"_L1, QByteArrayLiteral("Hello"));
+    row("prematureCharsetEnd", "data:charset,", true,
+        "charset", ""); // nonsense result, but don't crash
 }
 
 void tst_QDataUrl::decode()