diff --git a/src/frontends/lean/scanner.cpp b/src/frontends/lean/scanner.cpp
index 41b1184f9..ce7c2496a 100644
--- a/src/frontends/lean/scanner.cpp
+++ b/src/frontends/lean/scanner.cpp
@@ -348,40 +348,39 @@ auto scanner::read_key_cmd_id() -> token_kind {
             }
         }
     }
-
     unsigned i = 0;
-    token_table const * it  = find(*m_tokens, cs[i]);
+    token_table const * it  = m_tokens;
     token_info const * info = nullptr;
     unsigned key_sz       = 0;
     unsigned key_utf_sz   = 0;
-    unsigned aux_num_utfs = id_utf_sz;
-    if (it) {
-        if (aux_num_utfs == 0)
-            aux_num_utfs = 1;
-        info = value_of(*it);
-        if (info) {
+    while (i < id_sz) {
+        it = find(*it, cs[i]);
+        i++;
+        if (!it)
+            break;
+        if (auto new_info = value_of(*it)) {
             lean_assert(m_uskip == 0);
-            key_sz     = 1;
-            key_utf_sz = aux_num_utfs;
+            info       = new_info;
+            key_sz     = i;
+            key_utf_sz = id_utf_sz; // this is imprecise if key_sz < id_sz, but this case is irrelevant
         }
-        while (it) {
-            i++;
-            if (i == cs.size()) {
-                next_utf(cs);
-                num_utfs++;
-                aux_num_utfs = num_utfs;
-            }
-            it = find(*it, cs[i]);
-            if (it) {
-                if (auto new_info = value_of(*it)) {
-                    lean_assert(m_uskip == 0);
-                    info       = new_info;
-                    key_sz     = i+1;
-                    key_utf_sz = aux_num_utfs;
-                }
-            } else {
-                break;
-            }
+    }
+
+    while (it) {
+        if (i == cs.size()) {
+            next_utf(cs);
+            num_utfs++;
+        }
+        it = find(*it, cs[i]);
+        i++;
+        if (!it)
+            break;
+        if (auto new_info = value_of(*it)) {
+            lean_assert(m_uskip == 0);
+            info       = new_info;
+            key_sz     = i;
+            key_utf_sz = num_utfs;
+            lean_assert(key_sz > id_sz);
         }
     }
 
diff --git a/tests/lean/626c.lean b/tests/lean/626c.lean
new file mode 100644
index 000000000..27375a477
--- /dev/null
+++ b/tests/lean/626c.lean
@@ -0,0 +1,14 @@
+notation `C⁽` := nat
+definition foo (c : C⁽) := nat.rec_on c _ _
+
+notation `α⁽` := nat
+definition foo (c : α⁽) := nat.rec_on c _ _
+
+notation `_⁽` := nat
+definition foo (c : _⁽) := nat.rec_on c _ _
+
+notation `C.⁽` := nat
+definition foo (c : C.⁽) := nat.rec_on c _ _
+
+notation `C⁽C⁽` := nat
+definition foo (c : C⁽C⁽) := nat.rec_on c _ _
diff --git a/tests/lean/626c.lean.expected.out b/tests/lean/626c.lean.expected.out
new file mode 100644
index 000000000..e1c87b6ac
--- /dev/null
+++ b/tests/lean/626c.lean.expected.out
@@ -0,0 +1,70 @@
+626c.lean:2:27: error: don't know how to synthesize placeholder
+c : C⁽
+⊢ C⁽ → Type
+626c.lean:2:40: error: don't know how to synthesize placeholder
+c : C⁽
+⊢ ?M_1
+626c.lean:2:42: error: don't know how to synthesize placeholder
+c : C⁽
+⊢ Π (a : C⁽),
+    ?M_1 → ?M_1
+626c.lean:2:27: error: failed to add declaration 'foo' to environment, value has metavariables
+remark: set 'formatter.hide_full_terms' to false to see the complete term
+  λ (c : C⁽),
+    nat.rec_on c ?M_2 ?M_3
+626c.lean:5:27: error: don't know how to synthesize placeholder
+c : α⁽
+⊢ α⁽ → Type
+626c.lean:5:40: error: don't know how to synthesize placeholder
+c : α⁽
+⊢ ?M_1
+626c.lean:5:42: error: don't know how to synthesize placeholder
+c : α⁽
+⊢ Π (a : α⁽),
+    ?M_1 → ?M_1
+626c.lean:5:27: error: failed to add declaration 'foo' to environment, value has metavariables
+remark: set 'formatter.hide_full_terms' to false to see the complete term
+  λ (c : α⁽),
+    nat.rec_on c ?M_2 ?M_3
+626c.lean:8:27: error: don't know how to synthesize placeholder
+c : _⁽
+⊢ _⁽ → Type
+626c.lean:8:40: error: don't know how to synthesize placeholder
+c : _⁽
+⊢ ?M_1
+626c.lean:8:42: error: don't know how to synthesize placeholder
+c : _⁽
+⊢ Π (a : _⁽),
+    ?M_1 → ?M_1
+626c.lean:8:27: error: failed to add declaration 'foo' to environment, value has metavariables
+remark: set 'formatter.hide_full_terms' to false to see the complete term
+  λ (c : _⁽),
+    nat.rec_on c ?M_2 ?M_3
+626c.lean:11:28: error: don't know how to synthesize placeholder
+c : C.⁽
+⊢ C.⁽ → Type
+626c.lean:11:41: error: don't know how to synthesize placeholder
+c : C.⁽
+⊢ ?M_1
+626c.lean:11:43: error: don't know how to synthesize placeholder
+c : C.⁽
+⊢ Π (a : C.⁽),
+    ?M_1 → ?M_1
+626c.lean:11:28: error: failed to add declaration 'foo' to environment, value has metavariables
+remark: set 'formatter.hide_full_terms' to false to see the complete term
+  λ (c : C.⁽),
+    nat.rec_on c ?M_2 ?M_3
+626c.lean:14:29: error: don't know how to synthesize placeholder
+c : C⁽C⁽
+⊢ C⁽C⁽ → Type
+626c.lean:14:42: error: don't know how to synthesize placeholder
+c : C⁽C⁽
+⊢ ?M_1
+626c.lean:14:44: error: don't know how to synthesize placeholder
+c : C⁽C⁽
+⊢ Π (a : C⁽C⁽),
+    ?M_1 → ?M_1
+626c.lean:14:29: error: failed to add declaration 'foo' to environment, value has metavariables
+remark: set 'formatter.hide_full_terms' to false to see the complete term
+  λ (c : C⁽C⁽),
+    nat.rec_on c ?M_2 ?M_3