diff --git a/vllm/v1/engine/processor.py b/vllm/v1/engine/processor.py
index de15677aeea9..fbe8c8e3c793 100644
--- a/vllm/v1/engine/processor.py
+++ b/vllm/v1/engine/processor.py
@@ -29,7 +29,16 @@
 from vllm.v1.structured_output.backend_outlines import (
     validate_structured_output_request_outlines,
 )
-from vllm.v1.structured_output.backend_xgrammar import validate_xgrammar_grammar
+from vllm.v1.structured_output.utils import is_xgrammar_supported
+
+if is_xgrammar_supported():
+    from vllm.v1.structured_output.backend_xgrammar import validate_xgrammar_grammar
+else:
+    def validate_xgrammar_grammar(params):
+        raise ValueError(
+            "xgrammar is not supported on this platform. "
+            "Please use a different backend."
+        )
 
 logger = init_logger(__name__)
 
diff --git a/vllm/v1/structured_output/__init__.py b/vllm/v1/structured_output/__init__.py
index 6f9dbeabd8ca..7eaeef3c779f 100644
--- a/vllm/v1/structured_output/__init__.py
+++ b/vllm/v1/structured_output/__init__.py
@@ -14,7 +14,17 @@
     StructuredOutputBackend,
     StructuredOutputGrammar,
 )
-from vllm.v1.structured_output.backend_xgrammar import XgrammarBackend
+from vllm.v1.structured_output.utils import is_xgrammar_supported
+
+if is_xgrammar_supported():
+    from vllm.v1.structured_output.backend_xgrammar import XgrammarBackend
+else:
+    class XgrammarBackend:
+        def __init__(self, *args, **kwargs):
+            raise ValueError(
+                "xgrammar is not supported on this platform. "
+                "Cannot initialize XgrammarBackend."
+            )
 
 if TYPE_CHECKING:
     import numpy as np
diff --git a/vllm/v1/structured_output/utils.py b/vllm/v1/structured_output/utils.py
index e20ad1a6ec31..d567c824050e 100644
--- a/vllm/v1/structured_output/utils.py
+++ b/vllm/v1/structured_output/utils.py
@@ -13,6 +13,7 @@
 
 import vllm.envs as envs
 from vllm.logger import init_logger
+from vllm.platforms import CpuArchEnum, current_platform
 from vllm.utils.import_utils import LazyLoader
 
 if TYPE_CHECKING:
@@ -182,7 +183,7 @@ def get_outlines_cache():
 
 
 re_llama_byte_token = re.compile(r"^<0x[0-9A-F]{2}>$")
-re_replacement_seq = re.compile(r"^.{0,6}�+.{0,6}$")
+re_replacement_seq = re.compile(r"^.{0,6}\ufffd+.{0,6}$")
 
 
 def _reduced_vocabulary(
@@ -458,3 +459,8 @@ def escape_ebnf_string(s: str) -> str:
     escaped_choices = (escape_ebnf_string(c) for c in choice)
     grammar = "root ::= " + " | ".join(f'"{c}"' for c in escaped_choices)
     return grammar
+
+
+def is_xgrammar_supported() -> bool:
+    arch = current_platform.get_cpu_architecture()
+    return arch in (CpuArchEnum.X86, CpuArchEnum.ARM)