diff --git a/src/yunohost/domain.py b/src/yunohost/domain.py
index acd4a1131..e1d2b1649 100644
--- a/src/yunohost/domain.py
+++ b/src/yunohost/domain.py
@@ -89,6 +89,10 @@ def domain_add(operation_logger, domain, dyndns=False):
         raise YunohostError('domain_exists')
 
     operation_logger.start()
+    
+    # Lower domain to avoid some edge cases issues
+    # See: https://forum.yunohost.org/t/invalid-domain-causes-diagnosis-web-to-fail-fr-on-demand/11765
+    domain = domain.lower()
 
     # DynDNS domain
     if dyndns: