diff --git a/internal/gps/_testdata/src/canon_confl/README.md b/internal/gps/_testdata/src/canon_confl/README.md
new file mode 100644
index 0000000000..0e22451fb4
--- /dev/null
+++ b/internal/gps/_testdata/src/canon_confl/README.md
@@ -0,0 +1,3 @@
+The packages inside `vendor/` directoy contain bad go code. This "vendor"
+directory exists to avoid its content from being parsed by ListPackages when
+running on the whole dep code base.
diff --git a/internal/gps/_testdata/src/canon_confl/a.go b/internal/gps/_testdata/src/canon_confl/vendor/canon_confl/a.go
similarity index 100%
rename from internal/gps/_testdata/src/canon_confl/a.go
rename to internal/gps/_testdata/src/canon_confl/vendor/canon_confl/a.go
diff --git a/internal/gps/_testdata/src/canon_confl/b.go b/internal/gps/_testdata/src/canon_confl/vendor/canon_confl/b.go
similarity index 100%
rename from internal/gps/_testdata/src/canon_confl/b.go
rename to internal/gps/_testdata/src/canon_confl/vendor/canon_confl/b.go
diff --git a/internal/gps/pkgtree/pkgtree_test.go b/internal/gps/pkgtree/pkgtree_test.go
index fb1c0e8814..aa634f590c 100644
--- a/internal/gps/pkgtree/pkgtree_test.go
+++ b/internal/gps/pkgtree/pkgtree_test.go
@@ -1315,7 +1315,7 @@ func TestListPackages(t *testing.T) {
 			},
 		},
 		"conflicting canonical comments": {
-			fileRoot:   j("canon_confl"),
+			fileRoot:   j("canon_confl", "vendor", "canon_confl"),
 			importRoot: "canon_confl",
 			out:        PackageTree{},
 			err: &ConflictingImportComments{