diff --git a/asm/assembler_fuzz_test.go b/asm/assembler_fuzz_test.go
index a5a8101..6aa46fa 100644
--- a/asm/assembler_fuzz_test.go
+++ b/asm/assembler_fuzz_test.go
@@ -105,15 +105,12 @@ func FuzzAssembleAMD64(f *testing.F) {
 			}
 			return
 		}
-		// Determinism: a second parse-and-assemble from scratch must produce
-		// the same bytes, which also catches the assembler mutating the
-		// syntax tree it was handed.
-		file2, _ := parser.ParseWithOptions("fuzz_amd64.s", src,
-			parser.Options{Expand: true, IncludeDirs: fuzzIncludeDirs})
-		if file2 == nil {
-			t.Fatal("the second ParseWithOptions returned a nil file")
-		}
-		img2, err2 := AssembleFile(file2)
+		// Determinism: a second assembly of the same file must produce the
+		// same bytes.  One parse serves both runs, so any mutation the
+		// assembler makes to the syntax tree it was handed shows up as
+		// differing bytes, and the workers' footprint under the shared
+		// memory fence stays that of a single parse.
+		img2, err2 := AssembleFile(file)
 		if err2 != nil {
 			t.Fatalf("the second assembly failed where the first succeeded: %v", err2)
 		}