diff --git a/src/corelib/text/qstring.h b/src/corelib/text/qstring.h
index a1d130c2b17..f3759718bc8 100644
--- a/src/corelib/text/qstring.h
+++ b/src/corelib/text/qstring.h
@@ -316,7 +316,12 @@ public:
     [[nodiscard]] QString arg(T a, int fieldWidth = 0, int base = 10,
                               QChar fillChar = u' ') const
     {
-        if constexpr (std::is_signed_v<T>)
+        using U = typename std::conditional<
+                // underlying_type_t<non-enum> is UB in C++17/SFINAE in C++20, so wrap:
+                std::is_enum_v<T>, std::underlying_type<T>,
+                                   q20::type_identity<T>
+            >::type::type;
+        if constexpr (std::is_signed_v<U>)
             return arg_impl(qlonglong(a), fieldWidth, base, fillChar);
         else
             return arg_impl(qulonglong(a), fieldWidth, base, fillChar);
diff --git a/tests/auto/corelib/text/qstring/tst_qstring.cpp b/tests/auto/corelib/text/qstring/tst_qstring.cpp
index 11e2232133d..d4a041a6c15 100644
--- a/tests/auto/corelib/text/qstring/tst_qstring.cpp
+++ b/tests/auto/corelib/text/qstring/tst_qstring.cpp
@@ -6697,7 +6697,6 @@ void tst_QString::arg()
     // (unscoped) enums
     enum : int { FooS = -1 };
     enum : uint { FooU = 1 };
-    QEXPECT_FAIL("", "QTBUG-131906", Continue); // Qt 6.9 only
     QCOMPARE(s4.arg(FooS), QLatin1String("[-1]"));
     QCOMPARE(s4.arg(FooU), QLatin1String("[1]"));