diff --git a/libavcodec/s3tc.h b/libavcodec/s3tc.h
index ed385ae79ef6b8cc6c405edc17f2391d9e7b8779..b9808791d1d5afae1272c374b04caf1e1e528cbb 100644
--- a/libavcodec/s3tc.h
+++ b/libavcodec/s3tc.h
@@ -26,9 +26,25 @@
 #define FF_S3TC_DXT1    0x31545844
 #define FF_S3TC_DXT3    0x33545844
 
+/**
+ * Decode DXT1 encoded data to RGB32
+ * @param *src source buffer, has to be aligned on a 4-byte boundary
+ * @param *dst destination buffer
+ * @param w width of output image
+ * @param h height of output image
+ * @param stride line size of output image
+ */
 void ff_decode_dxt1(const uint8_t *src, uint8_t *dst,
                     const unsigned int w, const unsigned int h,
                     const unsigned int stride);
+/**
+ * Decode DXT3 encoded data to RGB32
+ * @param *src source buffer, has to be aligned on a 4-byte boundary
+ * @param *dst destination buffer
+ * @param w width of output image
+ * @param h height of output image
+ * @param stride line size of output image
+ */
 void ff_decode_dxt3(const uint8_t *src, uint8_t *dst,
                     const unsigned int w, const unsigned int h,
                     const unsigned int stride);