diff --git a/backend/src/api/nft_api.py b/backend/src/api/nft_api.py
index 0118e6a..95d0ac1 100644
--- a/backend/src/api/nft_api.py
+++ b/backend/src/api/nft_api.py
@@ -130,49 +130,49 @@ class BaseExpr(BaseModel):
         extra = "forbid"
 
 class MetaExpr(BaseExpr):
-    kind: Literal["meta"] = Field("meta", const=True)
+    kind: Literal["meta"] = Field(default="meta")
     key: MetaKey
     op: Op = Op.eq
     value: str
 
 class EtherExpr(BaseExpr):
-    kind: Literal["ether"] = Field("ether", const=True)
+    kind: Literal["ether"] = Field(default="ether")
     field: EtherField
     op: Op = Op.eq
     value: str
 
 class IPExpr(BaseExpr):
-    kind: Literal["ip"] = Field("ip", const=True)
+    kind: Literal["ip"] = Field(default="ip")
     side: IPDir
     op: Op = Op.eq
     value: str
 
 class ProtoPortExpr(BaseExpr):
-    kind: Literal["l4"] = Field("l4", const=True)
+    kind: Literal["l4"] = Field(default="l4")
     proto: Proto
     sport: Optional[str] = None
     dport: Optional[str] = None
 
 class CTEexpr(BaseExpr):
-    kind: Literal["ct"] = Field("ct", const=True)
+    kind: Literal["ct"] = Field(default="ct")
     state: ConntrackState
 
 class VerdictExpr(BaseExpr):
-    kind: Literal["verdict"] = Field("verdict", const=True)
+    kind: Literal["verdict"] = Field(default="verdict")
     verdict: Verdict
 
 class RejectExpr(BaseExpr):
-    kind: Literal["reject"] = Field("reject", const=True)
+    kind: Literal["reject"] = Field(default="reject")
     reject_type: RejectType
     icmp_type: Optional[IcmpType] = None
 
 class LogExpr(BaseExpr):
-    kind: Literal["log"] = Field("log", const=True)
+    kind: Literal["log"] = Field(default="log")
     prefix: Optional[str] = None
     group: Optional[LogGroup] = None
 
 class RawExpr(BaseExpr):
-    kind: Literal["raw"] = Field("raw", const=True)
+    kind: Literal["raw"] = Field(default="raw")
     snippet: str
 
 # Combine into a discriminated union