diff --git a/internal/cbm/extract_defs.c b/internal/cbm/extract_defs.c
index b49147dc6..d6de69ac0 100644
--- a/internal/cbm/extract_defs.c
+++ b/internal/cbm/extract_defs.c
@@ -5014,6 +5014,27 @@ static void push_method_def(CBMExtractCtx *ctx, TSNode child, TSNode class_node,
     cbm_defs_push(&ctx->result->defs, a, def);
 }
 
+/* Older C# grammars parse an extension declaration as a constructor whose body
+ * contains local functions. Recover those members without descending into
+ * ordinary C# method bodies. */
+static void extract_csharp_extension_members(CBMExtractCtx *ctx, TSNode node, TSNode class_node,
+                                             const char *class_qn, const CBMLangSpec *spec) {
+    const char *kind = ts_node_type(node);
+    if (strcmp(kind, "local_function_statement") == 0 || strcmp(kind, "method_declaration") == 0) {
+        TSNode name_node = resolve_method_name(node, ctx->language);
+        if (!ts_node_is_null(name_node)) {
+            push_method_def(ctx, node, class_node, class_qn, spec, name_node);
+        }
+        return;
+    }
+
+    uint32_t count = ts_node_named_child_count(node);
+    for (uint32_t i = 0; i < count; i++) {
+        extract_csharp_extension_members(ctx, ts_node_named_child(node, i), class_node, class_qn,
+                                         spec);
+    }
+}
+
 // Extract methods from an ObjC implementation_definition node.
 static void extract_objc_impl_methods(CBMExtractCtx *ctx, TSNode impl_node, const char *class_qn,
                                       const CBMLangSpec *spec) {
@@ -5132,6 +5153,14 @@ static void extract_class_methods(CBMExtractCtx *ctx, TSNode class_node, const c
             continue;
         }
 
+        if (ctx->language == CBM_LANG_CSHARP &&
+            strcmp(ts_node_type(method_node), "constructor_declaration") == 0) {
+            char *name = cbm_func_name_node_text(ctx->arena, name_node, ctx->source, ctx->language);
+            if (name && strcmp(name, "extension") == 0) {
+                extract_csharp_extension_members(ctx, method_node, class_node, class_qn, spec);
+                continue;
+            }
+        }
         push_method_def(ctx, method_node, class_node, class_qn, spec, name_node);
     }
 }
diff --git a/tests/test_grammar_labels.c b/tests/test_grammar_labels.c
index 7818c4c44..f2fff5eb0 100644
--- a/tests/test_grammar_labels.c
+++ b/tests/test_grammar_labels.c
@@ -93,6 +93,7 @@ static const LabelGolden LABEL_GOLDENS[] = {
     {"ruby", "Class:1,Function:1,Module:1"},
     {"php", "Class:1,Function:1,Module:1"},
     {"c_sharp", "Class:1,Method:1,Module:1"},
+    {"csharp_extension_declaration", "Class:1,Method:1,Module:1"},
     {"bash", "Function:2,Module:1"},
     {"zsh", "Function:2,Module:1"},
     {"lua", "Function:2,Module:1"},
diff --git a/tests/test_grammar_regression.c b/tests/test_grammar_regression.c
index 219c68edb..a8a786a0a 100644
--- a/tests/test_grammar_regression.c
+++ b/tests/test_grammar_regression.c
@@ -81,6 +81,20 @@ const GrammarCase CBM_GRAMMAR_CASES[] = {
      "class A {\n    void Foo() {}\n}\n",
      2,
      {"A", "Foo", NULL}},
+    {"csharp_extension_declaration",
+     CBM_LANG_CSHARP,
+     "Extensions.cs",
+     "using System.Collections.Generic;\n"
+     "using System.Linq;\n"
+     "public static class NumberExtensions\n"
+     "{\n"
+     "    extension(IEnumerable<int> numbers)\n"
+     "    {\n"
+     "        public int SumPositive() => numbers.Where(n => n > 0).Aggregate(0, static (total, n) => total + n);\n"
+     "    }\n"
+     "}\n",
+     2,
+     {"NumberExtensions", "SumPositive", NULL}},
     {"bash",
      CBM_LANG_BASH,
      "a.sh",