diff --git a/pkg/lang/treesitter/tags.go b/pkg/lang/treesitter/tags.go
index 799d96a..8018b28 100644
--- a/pkg/lang/treesitter/tags.go
+++ b/pkg/lang/treesitter/tags.go
@@ -85,6 +85,14 @@ var supplementalTagsQueries = map[string]string{
 	"cpp": strings.Join([]string{
 		"(namespace_definition name: (namespace_identifier) @name) @definition.module",
 	}, "\n"),
+	// gotreesitter's inferred C# tag query indexes interfaces, classes, and
+	// methods but drops `namespace_declaration` containers, the primary
+	// container for exported C# APIs. Capture both simple (identifier) and
+	// qualified namespace names as module definitions without disturbing any
+	// existing captures.
+	"c_sharp": strings.Join([]string{
+		"(namespace_declaration name: [(identifier) (qualified_name)] @name) @definition.module",
+	}, "\n"),
 }
 
 // ResolveTagsQuery returns the tree-sitter tags query canopy should use for a
diff --git a/pkg/lang/treesitter/tags_csharp_test.go b/pkg/lang/treesitter/tags_csharp_test.go
new file mode 100644
index 0000000..dca7fdd
--- /dev/null
+++ b/pkg/lang/treesitter/tags_csharp_test.go
@@ -0,0 +1,52 @@
+package treesitter
+
+import "testing"
+
+const csharpNamespaceSample = `namespace Acme.Telemetry
+{
+    public interface IClock
+    {
+        void Tick();
+    }
+
+    public class Clock : IClock
+    {
+        public void Tick() {}
+    }
+}
+
+namespace Utilities
+{
+    public class Parser {}
+}
+`
+
+func TestCSharpNamespaceDeclarationsIndexedAsModules(t *testing.T) {
+	entry := findEntryByExtension(t, ".cs")
+	parser, err := NewParser(entry)
+	if err != nil {
+		t.Fatalf("NewParser: %v", err)
+	}
+	summary, err := parser.Parse("sample.cs", []byte(csharpNamespaceSample))
+	if err != nil {
+		t.Fatalf("Parse: %v", err)
+	}
+
+	if !hasSymbol(summary, "interface_definition", "IClock") {
+		t.Error("missing C# interface IClock")
+	}
+	for _, cls := range []string{"Clock", "Parser"} {
+		if !hasSymbol(summary, "class_definition", cls) {
+			t.Errorf("missing C# class %s", cls)
+		}
+	}
+	if !hasSymbol(summary, "method_definition", "Tick") {
+		t.Error("missing C# methods Tick")
+	}
+	if !hasSymbol(summary, "module_definition", "Acme.Telemetry") {
+		t.Error("missing C# namespace Acme.Telemetry")
+	}
+	if !hasSymbol(summary, "module_definition", "Utilities") {
+		t.Error("missing C# namespace Utilities")
+	}
+}