diff --git a/cmake/modules/GtkDoc.cmake b/cmake/modules/GtkDoc.cmake
index 0ba1a7a78..2dfc4d691 100644
--- a/cmake/modules/GtkDoc.cmake
+++ b/cmake/modules/GtkDoc.cmake
@@ -98,6 +98,7 @@ macro(add_gtkdoc _module _namespace _deprecated_guards _srcdirsvar _depsvar _ign
 
 	# Add it as the last, thus in-tree headers have precedence
 	list(APPEND _scangobj_cflags_list -I${INCLUDE_INSTALL_DIR})
+	list(APPEND _scangobj_cflags_list ${CMAKE_C_FLAGS})
 
 	if(_scangobj_deps)
 		list(REMOVE_DUPLICATES _scangobj_deps)