diff --git a/packages/postgrest-react-query/src/mutate/use-upsert-mutation.ts b/packages/postgrest-react-query/src/mutate/use-upsert-mutation.ts
index 23ad4f651..78e38bf0c 100644
--- a/packages/postgrest-react-query/src/mutate/use-upsert-mutation.ts
+++ b/packages/postgrest-react-query/src/mutate/use-upsert-mutation.ts
@@ -53,6 +53,7 @@ function useUpsertMutation<
         query: query ?? undefined,
         queriesForTable,
         disabled: opts?.disableAutoQuery,
+        onConflict: primaryKeys.join(','),
         ...opts,
       })(input);
       if (data) {
diff --git a/packages/postgrest-swr/src/mutate/use-upsert-mutation.ts b/packages/postgrest-swr/src/mutate/use-upsert-mutation.ts
index 707ce1bdd..6ba75e823 100644
--- a/packages/postgrest-swr/src/mutate/use-upsert-mutation.ts
+++ b/packages/postgrest-swr/src/mutate/use-upsert-mutation.ts
@@ -56,6 +56,7 @@ function useUpsertMutation<
           query: query ?? undefined,
           queriesForTable,
           disabled: opts?.disableAutoQuery,
+          onConflict: primaryKeys.join(','),
           ...opts,
         },
       )(arg);