diff --git a/libavformat/rtp.h b/libavformat/rtp.h
index c46d0b8822..d142fff5e1 100644
--- a/libavformat/rtp.h
+++ b/libavformat/rtp.h
@@ -53,7 +53,7 @@ extern URLProtocol rtp_protocol;
 #define RTCP_TX_RATIO_NUM 5
 #define RTCP_TX_RATIO_DEN 1000
 
-/* Structure listing usefull vars to parse RTP packet payload*/
+/* Structure listing useful vars to parse RTP packet payload*/
 typedef struct rtp_payload_data_s
 {
     int sizelength;
diff --git a/libavutil/rational.h b/libavutil/rational.h
index 43fc22114f..140ce66822 100644
--- a/libavutil/rational.h
+++ b/libavutil/rational.h
@@ -56,7 +56,7 @@ static inline double av_q2d(AVRational a){
 
 /**
  * reduce a fraction.
- * this is usefull for framerate calculations
+ * This is useful for framerate calculations.
  * @param max the maximum allowed for dst_nom & dst_den
  * @return 1 if exact, 0 otherwise
  */