diff --git a/CMakeLists.txt b/CMakeLists.txt
index 159c4a24f..4cdc19911 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -250,6 +250,15 @@ message(STATUS "Update Translations: ${UPDATE_TRANSLATIONS}")
 
 include(FindQtRuntime)
 
+# Reject APIs that were deprecated before the oldest Qt release we support
+# (6.4). Qt 6.5 renamed the switch, so use whichever spelling the found
+# version understands while still compiling everywhere.
+if(Qt6_VERSION VERSION_GREATER_EQUAL 6.5)
+  add_compile_definitions(QT_DISABLE_DEPRECATED_UP_TO=0x060400)
+else()
+  add_compile_definitions(QT_DISABLE_DEPRECATED_BEFORE=0x060400)
+endif()
+
 set(CMAKE_AUTOMOC TRUE)
 
 # Find other needed libraries