diff --git a/src/corelib/text/qbytearray.h b/src/corelib/text/qbytearray.h
index 1e1a8c9c5e4..b7b33fa3ac1 100644
--- a/src/corelib/text/qbytearray.h
+++ b/src/corelib/text/qbytearray.h
@@ -495,12 +495,19 @@ public:
         // -1 to deal with the NUL terminator
         return Data::maxSize() - 1;
     }
-    inline qsizetype size() const noexcept { return d.size; }
+    constexpr qsizetype size() const noexcept
+    {
+#if __has_cpp_attribute(assume)
+        constexpr size_t MaxSize = maxSize();
+        [[assume(size_t(d.size) <= MaxSize)]];
+#endif
+        return d.size;
+    }
 #if QT_DEPRECATED_SINCE(6, 4)
     QT_DEPRECATED_VERSION_X_6_4("Use size() or length() instead.")
-    inline qsizetype count() const noexcept { return size(); }
+    constexpr qsizetype count() const noexcept { return size(); }
 #endif
-    inline qsizetype length() const noexcept { return size(); }
+    constexpr qsizetype length() const noexcept { return size(); }
     QT_CORE_INLINE_SINCE(6, 4)
     bool isNull() const noexcept;
 
diff --git a/src/corelib/text/qstring.h b/src/corelib/text/qstring.h
index b36ac709a2c..c1875688a48 100644
--- a/src/corelib/text/qstring.h
+++ b/src/corelib/text/qstring.h
@@ -232,12 +232,19 @@ public:
         // -1 to deal with the NUL terminator
         return Data::maxSize() - 1;
     }
-    inline qsizetype size() const noexcept { return d.size; }
+    constexpr qsizetype size() const noexcept
+    {
+#if __has_cpp_attribute(assume)
+        constexpr size_t MaxSize = maxSize();
+        [[assume(size_t(d.size) <= MaxSize)]];
+#endif
+        return d.size;
+    }
 #if QT_DEPRECATED_SINCE(6, 4)
     QT_DEPRECATED_VERSION_X_6_4("Use size() or length() instead.")
-    inline qsizetype count() const { return d.size; }
+    constexpr qsizetype count() const { return size(); }
 #endif
-    inline qsizetype length() const noexcept { return d.size; }
+    constexpr qsizetype length() const noexcept { return size(); }
     inline bool isEmpty() const noexcept { return d.size == 0; }
     void resize(qsizetype size);
     void resize(qsizetype size, QChar fillChar);
diff --git a/src/corelib/tools/qlist.h b/src/corelib/tools/qlist.h
index 81139c5891b..c9b931e420a 100644
--- a/src/corelib/tools/qlist.h
+++ b/src/corelib/tools/qlist.h
@@ -438,9 +438,16 @@ public:
 #endif // Q_QDOC
 
     static constexpr qsizetype maxSize() { return Data::maxSize(); }
-    qsizetype size() const noexcept { return d->size; }
-    qsizetype count() const noexcept { return size(); }
-    qsizetype length() const noexcept { return size(); }
+    constexpr qsizetype size() const noexcept
+    {
+#if __has_cpp_attribute(assume)
+        constexpr size_t MaxSize = maxSize();
+        [[assume(size_t(d.size) <= MaxSize)]];
+#endif
+        return d.size;
+    }
+    constexpr qsizetype count() const noexcept { return size(); }
+    constexpr qsizetype length() const noexcept { return size(); }
 
     inline bool isEmpty() const noexcept { return d->size == 0; }