diff --git a/src/frontends/lean/scanner.cpp b/src/frontends/lean/scanner.cpp
index 380bafb93..6f1479bc2 100644
--- a/src/frontends/lean/scanner.cpp
+++ b/src/frontends/lean/scanner.cpp
@@ -354,7 +354,7 @@ auto scanner::read_key_cmd_id() -> token_kind {
             } else if (cs[i] == '.') {
                 next_utf(cs);
                 num_utfs++;
-                if (!is_id_rest(cs, i+1))
+                if (!is_id_first(cs, i+1))
                     break;
             } else {
                 break;
diff --git a/tests/lean/bad_id.lean b/tests/lean/bad_id.lean
new file mode 100644
index 000000000..7dec22b98
--- /dev/null
+++ b/tests/lean/bad_id.lean
@@ -0,0 +1,5 @@
+import data.num
+
+definition x.y := 10
+
+definition x.1 := 10
diff --git a/tests/lean/bad_id.lean.expected.out b/tests/lean/bad_id.lean.expected.out
new file mode 100644
index 000000000..64eaa4cbd
--- /dev/null
+++ b/tests/lean/bad_id.lean.expected.out
@@ -0,0 +1 @@
+bad_id.lean:5:12: error: invalid binder, '(', '{', '[', '{{', '⦃' or identifier expected