diff --git a/animate2.cpp b/animate2.cpp
index a3a536e..2718b21 100644
--- a/animate2.cpp
+++ b/animate2.cpp
@@ -35,7 +35,7 @@ namespace animate2 {
     sequence.loop_count = 0;
     playing = true;
     sequence.timer.start();
-    sequence.frame_count = sequence.frames.size();
+    sequence.INVARIANT();
   }
 
   void Animate2::stop() {
@@ -96,9 +96,8 @@ namespace animate2 {
    * elapsed is DELTA, or use elapsed here?
    */
   void Animate2::update() {
-    dbc::check(sequence.easing_duration > 0.0, "bad easing duration");
     dbc::check(playing, "attempt to update animation that's not playing");
-    dbc::check(sequence.frame_count == sequence.frames.size(), "frame_count doesn't match frame.size()");
+    sequence.INVARIANT();
 
     auto [ticks, alpha] = sequence.timer.commit();
     int duration = sequence.durations.at(sequence.current);
@@ -119,16 +118,17 @@ namespace animate2 {
       sequence.loop_count++;
       sequence.easing_position = 0;
       playing = onLoop(sequence, transform);
+      sequence.INVARIANT();
     }
 
     if(frame_change) play_sound();
 
     if(frame_change && onFrame != nullptr) onFrame();
-
-    dbc::check(sequence.current < sequence.frame_count, "onLoop fail: current frame out of frames.size()");
   }
 
   void Animate2::motion(sf::Transformable& sprite, sf::Vector2f pos, sf::Vector2f scale) {
+    sequence.INVARIANT();
+
     transform.apply(sequence, pos, scale);
 
     if(transform.flipped) {
@@ -219,6 +219,8 @@ namespace animate2 {
     sequence = sequences.at(seq_name);
     transform = transforms.at(tr_name);
 
+    sequence.frame_count = sequence.frames.size();
+
     // BUG: should this be configurable instead?
     for(auto duration : sequence.durations) {
       sequence.easing_duration += float(duration);
@@ -228,6 +230,8 @@ namespace animate2 {
     $frame_rects = calc_frames();
     transform.easing_func = ease2::get_easing(transform.easing);
     transform.motion_func = ease2::get_motion(transform.motion);
+
+    sequence.INVARIANT();
   }
 
   Animate2 load(const std::string &file, const std::string &anim_name) {
@@ -245,4 +249,23 @@ namespace animate2 {
 
     return anim;
   }
+
+  void Sequence::INVARIANT(const std::source_location location) {
+    dbc::check(frames.size() == durations.size(),
+        fmt::format("frames.size={} doesn't match durations.size={}",
+          frames.size(), durations.size()), location);
+
+    dbc::check(easing_duration > 0.0,
+        fmt::format("bad easing duration: {}", easing_duration), location);
+
+    dbc::check(frame_count == frames.size(),
+        fmt::format("frame_count={} doesn't match frames.size={}", frame_count, frames.size()), location);
+
+    dbc::check(frame_count == durations.size(),
+        fmt::format("frame_count={} doesn't match durations.size={}", frame_count, durations.size()), location);
+
+    dbc::check(current < durations.size(),
+      fmt::format("current={} went past end of fame durations.size={}",
+        current, durations.size()), location);
+  }
 }
diff --git a/animate2.hpp b/animate2.hpp
index 15f9601..b02e5aa 100644
--- a/animate2.hpp
+++ b/animate2.hpp
@@ -11,6 +11,7 @@
 #include "ease2.hpp"
 #include <fmt/core.h>
 #include "json_mods.hpp"
+#include <source_location>
 
 namespace animate2 {
 
@@ -44,11 +45,13 @@ namespace animate2 {
     std::vector<int> durations{}; // in ticks
     size_t current{0};
     int loop_count{0};
-    size_t frame_count{0};
+    size_t frame_count{frames.size()};
     Timer timer{};
     int subframe{0};
     float easing_duration{0.0f};
     float easing_position{0.0f};
+
+    void INVARIANT(const std::source_location location = std::source_location::current());
   };
 
   struct Transform {
diff --git a/assets/animate2.json b/assets/animate2.json
index 327a5de..16f632e 100644
--- a/assets/animate2.json
+++ b/assets/animate2.json
@@ -8,7 +8,7 @@
     "sequences": {
       "idle": {"frames": [0], "durations": [47] },
       "hurt": {"frames": [0, 1], "durations": [5, 57] },
-      "attack": {"frames": [0, 1, 0, 1], "durations": [35, 15, 5, 5] }
+      "attack": {"frames": [0, 1, 0, 1], "durations": [35, 15, 5, 50] }
     },
     "transforms": {
       "rushing": {
diff --git a/tests/animate2.cpp b/tests/animate2.cpp
index 2c30fbb..6b37bcf 100644
--- a/tests/animate2.cpp
+++ b/tests/animate2.cpp
@@ -22,7 +22,11 @@ Animate2 load_animation(const string& name) {
   anim.set_form("attack");
 
   anim.transform.looped = false;
-  anim.sequence.durations = {Random::uniform(1, 5), Random::uniform(1, 5)};
+
+  for(size_t i = 0; i < anim.sequence.durations.size(); i++) {
+    anim.sequence.durations[i] = Random::uniform(1, 5);
+  }
+
   return anim;
 }
 
@@ -61,6 +65,12 @@ TEST_CASE("new animation system", "[animation-new]") {
   auto anim = load_animation("rat_king_boss");
   PLAY_TEST(anim);
 
+  // test that toggled works
+  anim.transform.toggled = true;
+  PLAY_TEST(anim);
+  REQUIRE(anim.sequence.current == anim.sequence.frames.size() - 1);
+  anim.transform.toggled = false;
+
   bool onLoop_ran = false;
   anim.onLoop = [&](auto& seq, auto& tr) -> bool {
     seq.current = 0;
@@ -84,16 +94,6 @@ TEST_CASE("new animation system", "[animation-new]") {
 
   PLAY_TEST(anim);
   REQUIRE(anim.sequence.loop_count == 2);
-
-  // stops at end
-  anim.onLoop = [](auto& seq, auto& tr) -> bool {
-    if(seq.loop_count == 1) {
-      seq.current = seq.frame_count - 1;
-      return false;
-    } else {
-      return true;
-    }
-  };
 }