diff --git a/main/utils.c b/main/utils.c
index 5d1855448c62f35ace567488276436501527be96..555800bcecd0df2f8489aa17c178981b1a7f6523 100644
--- a/main/utils.c
+++ b/main/utils.c
@@ -997,7 +997,14 @@ int ast_dynamic_str_thread_build_va(struct ast_dynamic_str **buf, size_t max_len
 			return AST_DYNSTR_BUILD_FAILED;
 		(*buf)->len = need;
 
-		/* Truncate the previous attempt. XXX this should be unconditional */
+		/* Truncate the previous attempt.  This is only needed for the
+		 * append operation because if the write is from the beginning,
+		 * it will get automatically overwritten when this function
+		 * gets called again.  When appending, if this was not done,
+		 * this function would be called over and over again, because
+		 * each attempt would be appending more and more partial
+		 * strings, never having enough space to finish.
+		 */ 
 		if (append)
 			(*buf)->str[offset] = '\0';