diff --git a/src/capwap/md5sum.c b/src/capwap/md5sum.c
index ecc5db7f..c1b1ac68 100644
--- a/src/capwap/md5sum.c
+++ b/src/capwap/md5sum.c
@@ -6,10 +6,17 @@
 
 #include "capwap_crypto.h"
 
-
 #define BLOCK_SIZE 4096
 
-
+/**
+ * Calculate MD5 checksum for an opened file. 
+ * @param digest destination buffer for calculated 
+ *   checksum (16 bytes, for a predifned constant use #CW_MD5_DIGEST_SIZE)
+ * @param infile filehanle 
+ * 
+ * Remember to set the file pointer to the beginning of the file, before
+ * calling this function. Therefor use fseek(file,0,SEEK_SET).
+ */
 int cw_fgetmd5sum(uint8_t *digest, FILE *infile)
 {
 	struct md5_ctx ctx;