diff --git a/cel-c/internal/BUILD b/cel-c/internal/BUILD
index c35cb69..a01675d 100644
--- a/cel-c/internal/BUILD
+++ b/cel-c/internal/BUILD
@@ -613,7 +613,9 @@ cc_library(
         "//cel-c:well_known_types",
         "@protobuf//upb/base",
         "@protobuf//upb/message",
+        "@protobuf//upb/message:message_unknowns",
         "@protobuf//upb/reflection",
+        "@protobuf//upb/wire",
         "@protobuf//upb/wire:eps_copy_input_stream",
         "@protobuf//upb/wire:reader",
     ],
@@ -635,6 +637,9 @@ cc_test(
         "@abseil-cpp//absl/log:die_if_null",
         "@abseil-cpp//absl/strings:string_view",
         "@abseil-cpp//absl/types:variant",
+        "@cel-spec//proto/cel/expr/conformance/proto2:test_all_types_cc_proto",
+        "@cel-spec//proto/cel/expr/conformance/proto2:test_all_types_upb_proto",
+        "@cel-spec//proto/cel/expr/conformance/proto2:test_all_types_upb_proto_reflection",
         "@cel-spec//proto/cel/expr/conformance/proto3:test_all_types_cc_proto",
         "@cel-spec//proto/cel/expr/conformance/proto3:test_all_types_upb_proto",
         "@cel-spec//proto/cel/expr/conformance/proto3:test_all_types_upb_proto_reflection",
@@ -654,6 +659,8 @@ cc_test(
         "@protobuf//:wrappers_upb_reflection_proto",
         "@protobuf//upb/base",
         "@protobuf//upb/message",
+        "@protobuf//upb/message:message_unknowns_testonly",
+        "@protobuf//upb/mini_table",
         "@protobuf//upb/reflection",
         "@protobuf//upb/wire",
     ],
diff --git a/cel-c/internal/message_equality.cc b/cel-c/internal/message_equality.cc
index 8d3f0a7..0c7f4cd 100644
--- a/cel-c/internal/message_equality.cc
+++ b/cel-c/internal/message_equality.cc
@@ -32,8 +32,10 @@
 #include "upb/message/array.h"
 #include "upb/message/map.h"
 #include "upb/message/message.h"
+#include "upb/message/unknown_fields.h"
 #include "upb/reflection/def.h"
 #include "upb/reflection/message.h"
+#include "upb/wire/encode.h"
 #include "upb/wire/eps_copy_input_stream.h"
 #include "upb/wire/reader.h"
 #include "upb/wire/types.h"
@@ -272,13 +274,25 @@ static _cel_UnknownFields* cel_nullable
 _cel_UnknownFields_FromMessage(_cel_MessageEqualityState* cel_nonnull state,
                                const upb_Message* cel_nonnull msg) {
   _cel_UnknownFields* fields = cel_nullptr;
-  cel_StringView unknown;
+  upb_MessageUnknown unknown;
   uintptr_t iter = kUpb_Message_UnknownBegin;
-  while (upb_Message_NextUnknown(msg, &unknown, &iter)) {
-    upb_EpsCopyInputStream_Init(&state->stream, &unknown.data,
-                                cel_StringView_Size(unknown));
-    fields = _cel_UnknownFields_Read(state, fields, &unknown.data);
-    CEL_ASSERT(upb_EpsCopyInputStream_IsDone(&state->stream, &unknown.data) &&
+  while (upb_Message_NextUnknown2(msg, &unknown, &iter)) {
+    upb_StringView bytes;
+    if (unknown.type == kUpb_MessageUnknownType_NonCanonicalExtension) {
+      cel_Arena* arena = _cel_MessageEqualityState_Arena(state);
+      upb_EncodeStatus status =
+          upb_MessageUnknown_Encode(unknown.value.extension, arena, &bytes);
+      if (CEL_UNLIKELY(status != kUpb_EncodeStatus_Ok)) {
+        _cel_MessageEqualityState_Throw(state,
+                                        _cel_MessageEquality_kOutOfMemory);
+      }
+    } else {
+      bytes = unknown.value.bytes;
+    }
+    const char* ptr = bytes.data;
+    upb_EpsCopyInputStream_Init(&state->stream, &ptr, bytes.size);
+    fields = _cel_UnknownFields_Read(state, fields, &ptr);
+    CEL_ASSERT(upb_EpsCopyInputStream_IsDone(&state->stream, &ptr) &&
                !upb_EpsCopyInputStream_IsError(&state->stream));
   }
   return fields;
diff --git a/cel-c/internal/message_equality_test.cc b/cel-c/internal/message_equality_test.cc
index ace2d46..0f19b66 100644
--- a/cel-c/internal/message_equality_test.cc
+++ b/cel-c/internal/message_equality_test.cc
@@ -44,6 +44,10 @@
 #include "cel-c/internal/config.h"
 #include "cel-c/status.h"
 #include "cel-c/well_known_types.h"
+#include "cel/expr/conformance/proto2/test_all_types.upb.h"
+#include "cel/expr/conformance/proto2/test_all_types.upbdefs.h"
+#include "cel/expr/conformance/proto2/test_all_types_extensions.upb.h"
+#include "cel/expr/conformance/proto2/test_all_types_extensions.upbdefs.h"
 #include "cel/expr/conformance/proto3/test_all_types.pb.h"
 #include "cel/expr/conformance/proto3/test_all_types.upbdefs.h"
 #include "google/protobuf/descriptor.h"
@@ -52,6 +56,8 @@
 #include "google/protobuf/unknown_field_set.h"
 #include "upb/message/array.h"
 #include "upb/message/message.h"
+#include "upb/message/unknown_fields_testonly.h"
+#include "upb/mini_table/extension.h"
 #include "upb/reflection/def.h"
 #include "upb/reflection/message.h"
 #include "upb/wire/decode.h"
@@ -2543,4 +2549,64 @@ INSTANTIATE_TEST_SUITE_P(
             },
         }));
 
+TEST(MessageEqualityTest_NonCanonical, Extensions) {
+  cel_Arena* arena = cel_Arena_New(cel_DefaultAllocator);
+  upb_DefPool* def_pool = upb_DefPool_New();
+  cel_Status status;
+  cel_Status_Construct(&status);
+
+  const upb_MessageDef* msg_def =
+      cel_expr_conformance_proto2_TestAllTypes_getmsgdef(def_pool);
+  ASSERT_NE(msg_def, nullptr);
+
+  cel_WellKnownTypes wkts;
+  ASSERT_TRUE(cel_WellKnownTypes_Initialize(&wkts, def_pool, &status));
+
+  const upb_MiniTable* mt = upb_MessageDef_MiniTable(msg_def);
+
+  // Msg 1
+  upb_Message* msg1 = upb_Message_New(mt, arena);
+  int32_t val1 = 42;
+  bool set1 = upb_Message_SetNonCanonicalExtension(
+      msg1, cel_expr_conformance_proto2_int32_ext_ext, &val1, arena);
+  ASSERT_TRUE(set1);
+
+  // Msg 2 (same extension, same value)
+  upb_Message* msg2 = upb_Message_New(mt, arena);
+  int32_t val2 = 42;
+  bool set2 = upb_Message_SetNonCanonicalExtension(
+      msg2, cel_expr_conformance_proto2_int32_ext_ext, &val2, arena);
+  ASSERT_TRUE(set2);
+
+  EXPECT_EQ(_cel_Message_Equals(msg1, msg2, msg_def, def_pool, &wkts,
+                                cel_DefaultAllocator),
+            _cel_MessageEquality_kEqual);
+
+  // Msg 3 (same extension, different value)
+  upb_Message* msg3 = upb_Message_New(mt, arena);
+  int32_t val3 = 43;
+  bool set3 = upb_Message_SetNonCanonicalExtension(
+      msg3, cel_expr_conformance_proto2_int32_ext_ext, &val3, arena);
+  ASSERT_TRUE(set3);
+
+  EXPECT_EQ(_cel_Message_Equals(msg1, msg3, msg_def, def_pool, &wkts,
+                                cel_DefaultAllocator),
+            _cel_MessageEquality_kNotEqual);
+
+  // Msg 4 (different extension: nested_ext)
+  upb_Message* msg4 = upb_Message_New(mt, arena);
+  const upb_Message* nested_msg = upb_Message_New(mt, arena);
+  bool set4 = upb_Message_SetNonCanonicalExtension(
+      msg4, cel_expr_conformance_proto2_nested_ext_ext, &nested_msg, arena);
+  ASSERT_TRUE(set4);
+
+  EXPECT_EQ(_cel_Message_Equals(msg1, msg4, msg_def, def_pool, &wkts,
+                                cel_DefaultAllocator),
+            _cel_MessageEquality_kNotEqual);
+
+  cel_Status_Destruct(&status);
+  upb_DefPool_Free(def_pool);
+  cel_Arena_Delete(arena);
+}
+
 }  // namespace