diff --git a/changelogs/fragments/40-mysql_user_fix_error_when_host_all_used.yml b/changelogs/fragments/40-mysql_user_fix_error_when_host_all_used.yml
new file mode 100644
index 0000000..8676e61
--- /dev/null
+++ b/changelogs/fragments/40-mysql_user_fix_error_when_host_all_used.yml
@@ -0,0 +1,2 @@
+bugfixes:
+- mysql_user - fix module's crash when modifying a user with ``host_all`` (https://github.com/ansible-collections/community.mysql/issues/39).
diff --git a/plugins/modules/mysql_user.py b/plugins/modules/mysql_user.py
index 8d6c36a..2cdc6a4 100644
--- a/plugins/modules/mysql_user.py
+++ b/plugins/modules/mysql_user.py
@@ -527,7 +527,7 @@ def user_mod(cursor, user, host, host_all, password, encrypted,
     old_user_mgmt = use_old_user_mgmt(cursor)
 
     if host_all:
-        hostnames = user_get_hostnames(cursor, [user])
+        hostnames = user_get_hostnames(cursor, user)
     else:
         hostnames = [host]
 
diff --git a/tests/integration/targets/test_mysql_user/tasks/main.yml b/tests/integration/targets/test_mysql_user/tasks/main.yml
index 04c90f3..0e9f7b4 100644
--- a/tests/integration/targets/test_mysql_user/tasks/main.yml
+++ b/tests/integration/targets/test_mysql_user/tasks/main.yml
@@ -196,6 +196,7 @@
         name: '{{ user_name_1 }}'
         priv: '%db.*:INSERT'
         append_privs: yes
+        host_all: yes
         password: '{{ user_password_1 }}'
 
     - name: show grants access for user1 on multiple database