diff --git a/cgo_harness/c26c_swift_mask_minimal.swift b/cgo_harness/c26c_swift_mask_minimal.swift
new file mode 100644
index 000000000..82de7eb86
--- /dev/null
+++ b/cgo_harness/c26c_swift_mask_minimal.swift
@@ -0,0 +1 @@
+let x = 1&<<7
diff --git a/cgo_harness/c26c_swift_masking_shift_probe_test.go b/cgo_harness/c26c_swift_masking_shift_probe_test.go
new file mode 100644
index 000000000..d4843223a
--- /dev/null
+++ b/cgo_harness/c26c_swift_masking_shift_probe_test.go
@@ -0,0 +1,116 @@
+//go:build cgo && treesitter_c_parity
+
+package cgoharness
+
+import (
+	"crypto/sha256"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	gotreesitter "github.com/odvcencio/gotreesitter"
+	"github.com/odvcencio/gotreesitter/internal/benchfixtures"
+	sitter "github.com/tree-sitter/go-tree-sitter"
+)
+
+func TestC26CMaskingShiftWitness(t *testing.T) {
+	tests := []struct {
+		name string
+		src  []byte
+	}{
+		{
+			name: "minimal",
+			src:  []byte("let x = 1&<<7\n"),
+		},
+		{
+			name: "corpus",
+			src: func() []byte {
+				path := filepath.Join("..", "grammars", "testdata", "swift_corpus", "stdlib_ASCII.swift")
+				src, err := os.ReadFile(path)
+				if err != nil {
+					panic(err)
+				}
+				return src
+			}(),
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			source := test.src
+			sourceDigest := sha256.Sum256(source)
+			goTree, goLang, err := parseWithGo(parityCase{name: "swift", source: string(source)}, source, nil)
+			if err != nil {
+				t.Fatalf("parse Swift with Go: %v", err)
+			}
+			defer releaseGoTree(goTree)
+
+			cLang, err := ParityCLanguage("swift")
+			if err != nil {
+				t.Fatalf("load locked Swift C parser: %v", err)
+			}
+			cParser := sitter.NewParser()
+			defer cParser.Close()
+			if err := cParser.SetLanguage(cLang); err != nil {
+				t.Fatalf("set locked Swift C parser language: %v", err)
+			}
+			cTree := cParser.Parse(source, nil)
+			if cTree == nil || cTree.RootNode() == nil {
+				t.Fatal("locked C parser returned no tree")
+			}
+			defer cTree.Close()
+
+			goRoot := goTree.RootNode()
+			cRoot := cTree.RootNode()
+			goInspection, err := benchfixtures.InspectGoTree(goRoot, goLang)
+			if err != nil {
+				t.Fatalf("inspect Go tree: %v", err)
+			}
+			cDigest, err := COracleDeepDigest(cTree)
+			if err != nil {
+				t.Fatalf("inspect C tree: %v", err)
+			}
+			diff := FirstDivergenceDumpV1(goRoot, goLang, cRoot)
+			t.Logf("C26C_MASK name=%s bytes=%d source_sha256=%x go_sha256=%s c_sha256=%s go_root=%d:%d go_children=%d go_error=%v c_root=%d:%d c_children=%d c_error=%v first_diff=%+v target=%d", test.name, len(source), sourceDigest, goInspection.SHA256, cDigest, goRoot.StartByte(), goRoot.EndByte(), goRoot.ChildCount(), goRoot.HasError(), cRoot.StartByte(), cRoot.EndByte(), int(cRoot.ChildCount()), cRoot.HasError(), diff, strings.Index(string(source), "1&<<7"))
+			c26cLogGoRootChildren(t, "go", goRoot, goLang, source)
+			c26cLogCRootChildren(t, "c", cRoot, source)
+		})
+	}
+}
+
+func c26cLogGoRootChildren(t *testing.T, label string, root *gotreesitter.Node, lang *gotreesitter.Language, source []byte) {
+	t.Helper()
+	limit := root.ChildCount()
+	if limit > 12 {
+		limit = 12
+	}
+	for i := 0; i < limit; i++ {
+		child := root.Child(i)
+		t.Logf("%s.root.child[%d] type=%q span=%d:%d named=%v extra=%v children=%d text=%s", label, i, child.Type(lang), child.StartByte(), child.EndByte(), child.IsNamed(), child.IsExtra(), child.ChildCount(), c26cText(source, child.StartByte(), child.EndByte()))
+	}
+}
+
+func c26cLogCRootChildren(t *testing.T, label string, root *sitter.Node, source []byte) {
+	t.Helper()
+	limit := int(root.ChildCount())
+	if limit > 12 {
+		limit = 12
+	}
+	for i := 0; i < limit; i++ {
+		child := root.Child(uint(i))
+		t.Logf("%s.root.child[%d] kind=%q span=%d:%d named=%v extra=%v children=%d text=%q", label, i, child.Kind(), child.StartByte(), child.EndByte(), child.IsNamed(), child.IsExtra(), int(child.ChildCount()), c26cText(source, uint32(child.StartByte()), uint32(child.EndByte())))
+	}
+}
+
+func c26cText(source []byte, start, end uint32) string {
+	if start > end || end > uint32(len(source)) {
+		return ""
+	}
+	text := string(source[start:end])
+	if len(text) > 100 {
+		text = text[:100]
+	}
+	return fmt.Sprintf("%q", text)
+}