diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -23,7 +23,7 @@
     GROUP_BASE_NAME KF
     VERSION ${KF5_VERSION}
     DEPRECATED_BASE_VERSION 0
-    DEPRECATION_VERSIONS 4.8 5.0 5.63 5.64 5.65
+    DEPRECATION_VERSIONS 4.8 5.0 5.63 5.64 5.65 5.66
     EXCLUDE_DEPRECATED_BEFORE_AND_AT ${EXCLUDE_DEPRECATED_BEFORE_AND_AT}
 )
 
diff --git a/src/kiconloader.h b/src/kiconloader.h
--- a/src/kiconloader.h
+++ b/src/kiconloader.h
@@ -707,11 +707,16 @@
 KICONTHEMES_EXPORT QIcon UserIconSet(const QString &name);
 #endif
 
+#if KICONTHEMES_ENABLE_DEPRECATED_SINCE(5, 66)
 /**
  * \relates KIconLoader
  * Returns the current icon size for a specific group.
+ * @deprecated since 5.66 Prefer QStyle::pixelMetric.
+ * If that's not an option for now, use KIconLoader::currentSize.
  */
+KICONTHEMES_DEPRECATED_VERSION(5, 66, "Use QStyle::pixelMetric or KIconLoader::currentSize")
 KICONTHEMES_EXPORT int IconSize(KIconLoader::Group group);
+#endif
 
 namespace KDE
 {
diff --git a/src/kiconloader.cpp b/src/kiconloader.cpp
--- a/src/kiconloader.cpp
+++ b/src/kiconloader.cpp
@@ -1778,11 +1778,13 @@
 }
 #endif
 
+#if KICONTHEMES_BUILD_DEPRECATED_SINCE(5, 66)
 int IconSize(KIconLoader::Group group)
 {
     KIconLoader *loader = KIconLoader::global();
     return loader->currentSize(group);
 }
+#endif
 
 QPixmap KIconLoader::unknown()
 {