diff --git a/Documentation/SOGoInstallationGuide.asciidoc b/Documentation/SOGoInstallationGuide.asciidoc
index 12bd7f2d8..4d631c671 100644
--- a/Documentation/SOGoInstallationGuide.asciidoc
+++ b/Documentation/SOGoInstallationGuide.asciidoc
@@ -1757,7 +1757,8 @@ Defaults to `YES` when unset.
 
 |ModulesConstraints (optional)
 |Limits the access of any module through a constraint based on a SQL
-column; must be a dictionary with keys `Mail`, and/or `Calendar`,
+column whose value is a string (e.g. `char` or `varchar` column type);
+must be a dictionary with keys `Mail`, and/or `Calendar`,
 and/or `ActiveSync` for example:
 
 ----