diff --git a/docs/reference/api-conventions.asciidoc b/docs/reference/api-conventions.asciidoc
index ef0b8f37958..efec2efe1a4 100644
--- a/docs/reference/api-conventions.asciidoc
+++ b/docs/reference/api-conventions.asciidoc
@@ -118,6 +118,7 @@ The special characters used for date rounding must be URI encoded as follows:
 `|`:: `%7C`
 `+`:: `%2B`
 `:`:: `%3A`
+`,`:: `%2C`
 ======================================================
 
 The following example shows different forms of date math index names and the final index names