diff --git a/src/storage.cr b/src/storage.cr
index 1dfe036..0715f8d 100644
--- a/src/storage.cr
+++ b/src/storage.cr
@@ -176,8 +176,11 @@ class DNSManager::Storage
 
 		domain = @domains_by_name.get domain_name
 		if domain.share_key.nil?
-			# Clone the domain so the database doesn't try to remove the new `shared_key`.
+			# Clone the domain so the database doesn't try to remove the new `share_key`.
 			domain_cloned = domain.clone
+
+			# Sharing the domain cancels domain transfer.
+			domain_cloned.transfer_key = nil
 			domain_cloned.share_key = UUID.random.to_s
 			@domains_by_name.update domain_name, domain_cloned
 			Response::DomainChanged.new domain_cloned
@@ -192,6 +195,9 @@ class DNSManager::Storage
 
 		domain = @domains_by_name.get domain_name
 		if domain.transfer_key.nil?
+			# You cannot transfer the domain in case it has a share key.
+			return Response::Error.new "The domain has a share key." unless domain.share_key.nil?
+
 			# Clone the domain so the database doesn't try to remove the new `transfer_key`.
 			domain_cloned = domain.clone
 			domain_cloned.transfer_key = UUID.random.to_s
@@ -209,7 +215,7 @@ class DNSManager::Storage
 
 		domain = @domains_by_name.get domain_name
 		if domain.owners.size == 1 && domain.owners[0] == user_id
-			# Clone the domain so the old `shared_key` still exists in the old version.
+			# Clone the domain so the old `share_key` still exists in the old version.
 			domain_cloned = domain.clone
 			domain_cloned.share_key = nil
 			@domains_by_name.update domain_cloned