diff --git a/Koha/Library.pm b/Koha/Library.pm
index 2fb7e4fef3..8056c70292 100644
--- a/Koha/Library.pm
+++ b/Koha/Library.pm
@@ -361,7 +361,7 @@ sub to_api_mapping {
         branchphone      => 'phone',
         branchfax        => 'fax',
         branchemail      => 'email',
-        branchillemail   => 'illemail',
+        branchillemail   => 'ill_email',
         branchreplyto    => 'reply_to_email',
         branchreturnpath => 'return_path_email',
         branchurl        => 'url',
diff --git a/api/v1/swagger/definitions/library.yaml b/api/v1/swagger/definitions/library.yaml
index 2d3f86d98f..0fc7967358 100644
--- a/api/v1/swagger/definitions/library.yaml
+++ b/api/v1/swagger/definitions/library.yaml
@@ -59,7 +59,7 @@ properties:
       - string
       - "null"
     description: the primary email address of the library
-  illemail:
+  ill_email:
     type:
       - string
       - "null"