diff --git a/libswscale/swscale.h b/libswscale/swscale.h
index abc23fcf40..9a088af3fc 100644
--- a/libswscale/swscale.h
+++ b/libswscale/swscale.h
@@ -112,6 +112,10 @@ typedef struct {
 
 struct SwsContext;
 
+/**
+ * Frees the swscaler context swsContext.
+ * If swsContext is NULL, then does nothing.
+ */
 void sws_freeContext(struct SwsContext *swsContext);
 
 /**