diff --git a/tokenlists/typing.py b/tokenlists/typing.py
index 1b04c57..b85991d 100644
--- a/tokenlists/typing.py
+++ b/tokenlists/typing.py
@@ -55,25 +55,39 @@ class TokenInfo(BaseModel):
     tags: Optional[List[TagId]] = None
     extensions: Optional[Dict[str, Any]] = None
 
-    @validator("extensions")
-    def parse_extensions(cls, v: dict):
-        if "bridgeInfo" in v:
+    @validator("extensions", pre=True)
+    def parse_extensions(cls, v: Optional[Dict[str, Any]]) -> Optional[Dict[str, Any]]:
+        # 1. Check extension depth first
+        def extension_depth(obj: Optional[Dict[str, Any]]) -> int:
+            if not isinstance(obj, dict) or len(obj) == 0:
+                return 0
+
+            return 1 + max(extension_depth(v) for v in obj.values())
+
+        if (depth := extension_depth(v)) > 3:
+            raise ValueError(f"Extension depth is greater than 3: {depth}")
+
+        # 2. Parse valid extensions
+        if v and "bridgeInfo" in v:
             v["bridgeInfo"] = BridgeInfo.parse_obj(v.pop("bridgeInfo"))
 
         return v
 
     @validator("extensions")
-    def check_extension_depth(cls, v: dict):
-        def extension_depth(obj: dict) -> int:
-            depth = 0
-            for v in obj.values():
-                if isinstance(v, dict):
-                    depth = max(depth, extension_depth(v))
+    def extensions_must_contain_allowed_types(
+        cls, d: Optional[Dict[str, Any]]
+    ) -> Optional[Dict[str, Any]]:
+        if not d:
+            return d
 
-            return depth + 1
+        # NOTE: `extensions` is mapping from `str` to either:
+        #       - a parsed `dict` type (e.g. `BaseModel`)
+        #       - a "simple" type (e.g. string, integer or boolean value)
+        for key, val in d.items():
+            if not isinstance(val, (BaseModel, str, int, bool)) and val is not None:
+                raise ValueError(f"Incorrect extension field value: {val}")
 
-        assert extension_depth(v) < 3
-        return v
+        return d
 
     @property
     def bridge_info(self) -> Optional[BridgeInfo]:
@@ -101,21 +115,6 @@ def decimals_must_be_uint8(cls, v: TokenDecimals):
 
         return v
 
-    @validator("extensions")
-    def extensions_must_contain_simple_types(cls, d: Optional[dict]) -> Optional[dict]:
-        if not d:
-            return d
-
-        # `extensions` is `Dict[str, Union[str, int, bool, None]]`, but pydantic mutates entries
-        for key, val in d.items():
-            if key in "bridgeInfo":
-                continue  # don't parse valid extensions
-
-            if not isinstance(val, (str, int, bool)) and val is not None:
-                raise ValueError(f"Incorrect extension field value: {val}")
-
-        return d
-
 
 class Tag(BaseModel):
     name: str