diff --git a/src/poetry/core/version/grammars/markers.lark b/src/poetry/core/version/grammars/markers.lark
index 189ab02a5..e0079c2a2 100644
--- a/src/poetry/core/version/grammars/markers.lark
+++ b/src/poetry/core/version/grammars/markers.lark
@@ -15,7 +15,6 @@ MARKER_NAME: "implementation_version"
     | "platform_system"
     | "python_version"
     | "sys_platform"
-    | "sys_platform"
     | "os_name"
     | "os.name"
     | "sys.platform"