diff --git a/mysql-test/suite/plugins/r/server_audit_bugs.result b/mysql-test/suite/plugins/r/server_audit_bugs.result
new file mode 100644
index 00000000000..63e007f266b
--- /dev/null
+++ b/mysql-test/suite/plugins/r/server_audit_bugs.result
@@ -0,0 +1,20 @@
+#
+# MDEV-34074 server_audit crashes in get_loc_info() with NULL loc_info
+#
+INSTALL PLUGIN server_audit SONAME 'server_audit';
+UNINSTALL PLUGIN server_audit;
+Warnings:
+Warning	1620	Plugin is busy and will be uninstalled on shutdown
+connect  con1,localhost,root,,;
+DO @@session.aria_repair_threads;
+connection default;
+INSTALL PLUGIN server_audit SONAME 'server_audit';
+connection con1;
+SELECT 1;
+1
+1
+connection default;
+disconnect con1;
+UNINSTALL PLUGIN server_audit;
+Warnings:
+Warning	1620	Plugin is busy and will be uninstalled on shutdown
diff --git a/mysql-test/suite/plugins/t/server_audit_bugs.test b/mysql-test/suite/plugins/t/server_audit_bugs.test
new file mode 100644
index 00000000000..1b37a7b74ac
--- /dev/null
+++ b/mysql-test/suite/plugins/t/server_audit_bugs.test
@@ -0,0 +1,32 @@
+--source include/not_embedded.inc
+
+if (!$SERVER_AUDIT_SO) {
+  skip No SERVER_AUDIT plugin;
+}
+
+--echo #
+--echo # MDEV-34074 server_audit crashes in get_loc_info() with NULL loc_info
+--echo #
+# THDVAR() could return NULL if the plugin was previously uninstalled -
+# uninstall wipes the session-variable placeholders and they are not
+# reinitialized on re-install. Black magic to reproduce: install and
+# uninstall server_audit, create a new session and touch any plugin session
+# variable (aria_repair_threads), then install server_audit again.
+# The "will be uninstalled on shutdown" warning below is misleading: the
+# plugin is actually reaped as soon as its last reference drops (which is
+# what wipes the placeholders), not on shutdown.
+INSTALL PLUGIN server_audit SONAME 'server_audit';
+UNINSTALL PLUGIN server_audit;
+
+connect (con1,localhost,root,,);
+DO @@session.aria_repair_threads;
+
+connection default;
+INSTALL PLUGIN server_audit SONAME 'server_audit';
+
+connection con1;
+SELECT 1;
+
+connection default;
+disconnect con1;
+UNINSTALL PLUGIN server_audit;
diff --git a/plugin/server_audit/server_audit.c b/plugin/server_audit/server_audit.c
index 5d37186aeaa..1697441a34c 100644
--- a/plugin/server_audit/server_audit.c
+++ b/plugin/server_audit/server_audit.c
@@ -839,7 +839,8 @@ static struct connection_info *get_loc_info(MYSQL_THD thd)
   return (struct connection_info *) THDVAR(thd, loc_info);
   */
   struct connection_info *ci= (struct connection_info *) THDVAR(thd, loc_info);
-  if ((size_t) ci->user_length > sizeof(ci->user))
+  /* THDVAR can return NULL if the plugin was previously uninstalled (MDEV-34074). */
+  if (ci && (size_t) ci->user_length > sizeof(ci->user))
   {
     ci->user_length= 0;
     ci->host_length= 0;
@@ -2073,7 +2074,9 @@ void auditing(MYSQL_THD thd, unsigned int event_class, const void *ev)
     cn= get_loc_info(thd);
   }
 
-  update_connection_info(thd, cn, event_class, ev, &after_action);
+  /* Without loc_info (see get_loc_info) the session is not audited. */
+  if (cn)
+    update_connection_info(thd, cn, event_class, ev, &after_action);
 
   if (!logging)
   {
@@ -2631,7 +2634,7 @@ static void log_current_query(MYSQL_THD thd)
   if (!thd)
     return;
   cn= get_loc_info(thd);
-  if (!ci_needs_setup(cn) && cn->query_length)
+  if (cn && !ci_needs_setup(cn) && cn->query_length)
   {
     cn->log_always= 1;
     log_statement_ex(cn, cn->query_time, thd_get_thread_id(thd),