idiff --git a/syncstorage-mysql/src/diesel_ext.rs b/syncstorage-mysql/src/diesel_ext.rs
index 18abb4a..fe52470 100644
--- a/syncstorage-mysql/src/diesel_ext.rs
+++ b/syncstorage-mysql/src/diesel_ext.rs
@@ -3,11 +3,43 @@ use std::{fmt::Debug, marker::PhantomData};
 use diesel::{
     backend::Backend,
     insertable::CanInsertInSingleQuery,
+    mysql::Mysql,
     query_builder::{AstPass, InsertStatement, QueryFragment, QueryId},
+    query_dsl::methods::LockingDsl,
     result::QueryResult,
     Expression, QuerySource, RunQueryDsl,
 };

+/// Emit MySQL <= 5.7's `LOCK IN SHARE MODE`
+///
+/// MySQL 8 supports `FOR SHARE` as an alias (which diesel natively supports)
+pub trait LockInShareModeDsl {
+    type Output;
+
+    fn lock_in_share_mode(self) -> Self::Output;
+}
+
+impl<T> LockInShareModeDsl for T
+where
+    T: LockingDsl<LockInShareMode>,
+{
+    type Output = <T as LockingDsl<LockInShareMode>>::Output;
+
+    fn lock_in_share_mode(self) -> Self::Output {
+        self.with_lock(LockInShareMode)
+    }
+}
+
+#[derive(Debug, Clone, Copy, QueryId)]
+pub struct LockInShareMode;
+
+impl QueryFragment<Mysql> for LockInShareMode {
+    fn walk_ast<'b>(&'b self, mut out: AstPass<'_, 'b, Mysql>) -> QueryResult<()> {
+        out.push_sql(" LOCK IN SHARE MODE");
+        Ok(())
+    }
+}
+
 #[allow(dead_code)] // Not really dead, Rust can't see it.
 #[derive(Debug, Clone)]
 pub struct OnDuplicateKeyUpdate<T, U, Op, Ret, DB, X>(
diff --git a/syncstorage-mysql/src/models.rs b/syncstorage-mysql/src/models.rs
index 1114f21..fb54649 100644
--- a/syncstorage-mysql/src/models.rs
+++ b/syncstorage-mysql/src/models.rs
@@ -25,6 +25,7 @@ use syncstorage_settings::{Quota, DEFAULT_MAX_TOTAL_RECORDS};

 use super::{
     batch,
+    diesel_ext::LockInShareModeDsl,
     error::DbError,
     pool::{CollectionCache, Conn},
     schema::{bso, collections, user_collections},
@@ -179,7 +180,7 @@ impl MysqlDb {
             .select(user_collections::modified)
             .filter(user_collections::user_id.eq(user_id))
             .filter(user_collections::collection_id.eq(collection_id))
-            .for_share()
+            .lock_in_share_mode()
             .first(&mut *self.conn.write()?)
             .optional()?;
         if let Some(modified) = modified {