diff --git a/internal/cbm/resolve/adapter_swift.c b/internal/cbm/resolve/adapter_swift.c
index 03dafa370..8fa01cbb5 100644
--- a/internal/cbm/resolve/adapter_swift.c
+++ b/internal/cbm/resolve/adapter_swift.c
@@ -41,6 +41,7 @@
 #include "source_adapter_internal.h"
 #include <stdio.h>
 #include <stdlib.h>
+#include "stats.h"
 #include "syntax_index.h"
 
 #define SWIFT_TYPE_RECORD "&type"
@@ -1221,8 +1222,8 @@ static swift_lookup_t swift_find_member(swift_ctx_t *ctx, const char *type_key,
     }
     /* Only extensions here: what the extension spells is declared elsewhere, or outside. */
     bool extension_only = true;
-    for (const cbm_source_decl_t *record = records; record; record = record->next)
-        extension_only &= (record->flags & CBM_SOURCE_DECL_F_ADAPTED) != 0;
+    for (const cbm_source_decl_t *record = records; record && extension_only; record = record->next)
+        extension_only = (record->flags & CBM_SOURCE_DECL_F_ADAPTED) != 0;
     bool declared = false;
     if (extension_only && !bases_only) {
         const char *hash = strchr(type_key, '#');
@@ -1255,8 +1256,12 @@ static swift_lookup_t swift_find_member(swift_ctx_t *ctx, const char *type_key,
     /* An extension of a type outside the project has no declaration here. */
     const char *base_owner = type_key;
     for (const cbm_source_decl_t *record = records; record; record = record->next) {
+        cbm_resolve_stats_add(CBM_RESOLVE_STAT_LOOKUP_PROBES, 1);
         declared |= !(record->flags & CBM_SOURCE_DECL_F_ADAPTED);
         open |= (record->flags & CBM_SOURCE_DECL_F_OPEN) != 0;
+        /* Past the chain's bound every further base answers open, and the answer is open now. */
+        if (open && chain->overflow)
+            break;
         for (const char *const *base = record->bases; base && *base; base++) {
             const char *parent = swift_lookup_type(ctx, base_owner, *base);
             if (!parent) {
diff --git a/tests/test_complexity.c b/tests/test_complexity.c
index d9a86def6..d3dc2bfdc 100644
--- a/tests/test_complexity.c
+++ b/tests/test_complexity.c
@@ -3263,6 +3263,16 @@ TEST(complexity_source_same_named_definitions_are_near_linear) {
     PASS();
 }
 
+/* `extension A: P` many times over: a name found in none of A's bases asks each of them. */
+CX_LINE3(cx_line_swift_extension_base,
+         "protocol P%d {}\nextension A: P%d {\n  func m_%d() { base() }\n}\n")
+TEST(complexity_swift_type_bases_are_near_linear) {
+    ASSERT_TRUE(cx_source_shape_is_near_linear(CBM_LANG_SWIFT, "bases.swift",
+                                               "class A { func base() {} }\n",
+                                               cx_line_swift_extension_base, ""));
+    PASS();
+}
+
 /* A barrel library re-exports the project, and every library that imports it read its whole
  * export list again. */
 static uint64_t cx_dart_barrel_work(int libraries) {
@@ -3457,6 +3467,7 @@ SUITE(complexity) {
     RUN_TEST(complexity_syntax_index_prev_siblings_answer_as_tree_sitter_does);
     RUN_TEST(complexity_prev_sibling_walk_is_linear);
     RUN_TEST(complexity_source_same_named_definitions_are_near_linear);
+    RUN_TEST(complexity_swift_type_bases_are_near_linear);
     RUN_TEST(complexity_dart_barrel_exports_are_near_linear);
     RUN_TEST(complexity_go_route_bindings_are_near_linear);
     RUN_TEST(complexity_flat_preceding_label_is_linear);