diff --git a/ci/test-indent/test_backslash_ops.v b/ci/test-indent/test_backslash_ops.v
new file mode 100644
index 000000000..b350f2fb0
--- /dev/null
+++ b/ci/test-indent/test_backslash_ops.v
@@ -0,0 +1,19 @@
+Require Import mathcomp.ssreflect.ssrbool.
+
+Definition xx := nat.
+Module foo.
+  (* from PG issue #757 *)
+  Lemma test:
+    forall a : nat,
+      a \in [::] ->  (* "\in" should be detected as one token *)
+      False.
+  Proof.
+  Abort.
+
+  Lemma test2:
+    forall a : nat,
+      a \in  (* "\in" should be detected as one token *)
+        [::] ->
+      False.
+End foo.
+