diff --git a/Cargo.lock b/Cargo.lock
index 813ed2f..9b1dfd6 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -778,9 +778,9 @@ dependencies = [
 
 [[package]]
 name = "syn"
-version = "2.0.36"
+version = "2.0.37"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "91e02e55d62894af2a08aca894c6577281f76769ba47c94d5756bec8ac6e7373"
+checksum = "7303ef2c05cd654186cb250d29049a24840ca25d2747c25c0381c8d9e2f582e8"
 dependencies = [
  "proc-macro2",
  "quote",
diff --git a/build.rs b/build.rs
index f51dc40..2a1c444 100644
--- a/build.rs
+++ b/build.rs
@@ -43,6 +43,7 @@ fn main() {
         } = skill;
         let hits = quote_option(hits);
         let expected = quote_option(expected);
+        let max_duration = quote_option(max_duration);
         quote! {
             SkillDef {
                 id: #id,
diff --git a/src/data/structs.rs b/src/data/structs.rs
index aec8601..479e5ff 100644
--- a/src/data/structs.rs
+++ b/src/data/structs.rs
@@ -4,6 +4,9 @@ use serde::{Deserialize, Serialize};
 // TODO: instead of hits allow counting buff apply?
 // TODO: support instant casts with buff apply?
 
+/// Extra error margin for max duration.
+const DURATION_EPSILON: i32 = 500;
+
 /// Skill information.
 #[derive(Debug, Clone)]
 pub struct SkillInfo {
@@ -37,7 +40,9 @@ impl From<SkillDef> for SkillInfo {
                 max,
                 expected: expected.unwrap_or((max + 1) / 2),
             }),
-            max_duration,
+            max_duration: max_duration
+                .map(|dur| dur + DURATION_EPSILON)
+                .unwrap_or(i32::MAX),
             minion,
         }
     }
@@ -74,18 +79,13 @@ pub struct SkillDef {
     pub expected: Option<usize>,
 
     /// Maximum duration (ms) to count as one cast.
-    #[serde(default = "default_as_max")]
-    pub max_duration: i32,
+    pub max_duration: Option<i32>,
 
     /// Whether to include minion hits.
     #[serde(default)]
     pub minion: bool,
 }
 
-const fn default_as_true() -> bool {
+fn default_as_true() -> bool {
     true
 }
-
-const fn default_as_max() -> i32 {
-    i32::MAX
-}
diff --git a/src/plugin/event.rs b/src/plugin/event.rs
index b8edae3..55b3185 100644
--- a/src/plugin/event.rs
+++ b/src/plugin/event.rs
@@ -8,9 +8,6 @@ use crate::combat::{
 use arcdps::{evtc::EventKind, Activation, Agent, CombatEvent, StateChange, Strike};
 use log::debug;
 
-/// Extra error margin for max duration.
-const DURATION_EPSILON: i32 = 500;
-
 impl Plugin {
     /// Handles a combat event from area stats.
     pub fn area_event(
@@ -205,7 +202,7 @@ impl Plugin {
                 // replace skill id
                 skill.id = info.id;
 
-                let max = info.max_duration + DURATION_EPSILON;
+                let max = info.max_duration;
                 match self.latest_cast_mut(skill.id) {
                     Some(cast) if time - cast.time <= max => {
                         cast.hit(target);