diff --git a/src/corelib/text/qlocale.cpp b/src/corelib/text/qlocale.cpp
index a3429ec9f8..3ce1f501c4 100644
--- a/src/corelib/text/qlocale.cpp
+++ b/src/corelib/text/qlocale.cpp
@@ -558,7 +558,7 @@ bool qt_splitLocaleName(QStringView name, QStringView *lang, QStringView *script
             state = NoState;
             break;
         case NoState: // Precluded by loop condition !
-            Q_ASSERT(!"QLocale: This should never happen");
+            Q_UNREACHABLE();
             break;
         }
     }
diff --git a/src/corelib/text/qlocale_tools.cpp b/src/corelib/text/qlocale_tools.cpp
index 4421d40340..a8f63a5998 100644
--- a/src/corelib/text/qlocale_tools.cpp
+++ b/src/corelib/text/qlocale_tools.cpp
@@ -530,7 +530,8 @@ QString qulltoa(qulonglong number, int base, const QStringView zero)
 
             number /= base;
         }
-    } else {
+    } else { // zero should always be either a non-surrogate or a surrogate pair:
+        Q_UNREACHABLE();
         return QString();
     }