diff --git a/app/db/crud.py b/app/db/crud.py
index f846ebc..963a3bd 100644
--- a/app/db/crud.py
+++ b/app/db/crud.py
@@ -439,6 +439,16 @@ def update_user(
     if modify.expire_strategy is not None:
         dbuser.expire_strategy = modify.expire_strategy or None
 
+        if modify.expire_strategy == UserExpireStrategy.FIXED_DATE:
+            dbuser.usage_duration = None
+            dbuser.activation_deadline = None
+        elif modify.expire_strategy == UserExpireStrategy.START_ON_FIRST_USE:
+            dbuser.expire_date = None
+        elif modify.expire_strategy == UserExpireStrategy.NEVER:
+            dbuser.expire_date = None
+            dbuser.usage_duration = None
+            dbuser.activation_deadline = None
+
     if modify.expire_date is not None:
         dbuser.expire_date = modify.expire_date or None
 
diff --git a/app/models/user.py b/app/models/user.py
index 1da44de..60a8048 100644
--- a/app/models/user.py
+++ b/app/models/user.py
@@ -61,6 +61,35 @@ class User(BaseModel):
 
     model_config = ConfigDict(from_attributes=True)
 
+    @model_validator(mode="after")
+    def validate_expiry(self):
+        if self.expire_strategy == UserExpireStrategy.START_ON_FIRST_USE:
+            if not self.usage_duration:
+                raise ValueError(
+                    "User expire_strategy cannot be start_on_first_use without a valid usage_duration."
+                )
+
+            # Set expire_date to None if expire_strategy is START_ON_FIRST_USE
+            self.expire_date = None
+
+        elif self.expire_strategy == UserExpireStrategy.FIXED_DATE:
+            if not self.expire_date:
+                raise ValueError(
+                    "User expire_strategy cannot be fixed_date without a valid expire date."
+                )
+
+            # Set usage_duration and activation_deadline to None if expire_strategy is START_ON_FIRST_USE
+            self.usage_duration = None
+            self.activation_deadline = None
+
+        elif self.expire_strategy == UserExpireStrategy.NEVER:
+            # Set expire_date, usage_duration and activation_deadline to None if expire_strategy is NEVER
+            self.expire_date = None
+            self.usage_duration = None
+            self.activation_deadline = None
+
+        return self
+
 
 class UserCreate(User):
     service_ids: list[int] = Field([])
@@ -79,22 +108,6 @@ class UserCreate(User):
         }
     )
 
-    @model_validator(mode="after")
-    def validate_expiry(self):
-        if self.expire_strategy == UserExpireStrategy.START_ON_FIRST_USE:
-            if not self.usage_duration:
-                raise ValueError(
-                    "User expire_strategy can not be start_on_first_use without a valid usage_duration."
-                )
-        elif (
-            self.expire_strategy == UserExpireStrategy.FIXED_DATE
-            and not self.expire_date
-        ):
-            raise ValueError(
-                "User expire_strategy can not be fixed_date without a valid expire date."
-            )
-        return self
-
 
 class UserModify(UserCreate):
     service_ids: list[int] | None = Field(None)