diff --git a/libavutil/cpu.h b/libavutil/cpu.h
index bb80c8d76a..e448da6cdc 100644
--- a/libavutil/cpu.h
+++ b/libavutil/cpu.h
@@ -53,6 +53,7 @@ int av_get_cpu_flags(void);
 
 /**
  * Disables cpu detection and forces the specified flags.
+ * -1 is a special case that disables forcing of specific flags.
  */
 void av_force_cpu_flags(int flags);