diff --git a/src/compiler/iroptimizer.js b/src/compiler/iroptimizer.js
index d3bbbeaf..91ebd5cf 100644
--- a/src/compiler/iroptimizer.js
+++ b/src/compiler/iroptimizer.js
@@ -565,6 +565,11 @@ class IROptimizer {
             this.addPossibleExitState(state);
             break;
         }
+        case StackOpcode.CONTROL_WAIT_UNTIL: {
+            modified = state.clear() || modified;
+            modified = this.analyzeInputs(inputs, state) || modified;
+            break;
+        }
         case StackOpcode.PROCEDURE_CALL: {
             modified = this.analyzeInputs(inputs, state) || modified;
             modified = this.analyzeInputs(inputs.inputs, state) || modified;
diff --git a/test/fixtures/execute/tw-wait-until-condition-gh-277.sb3 b/test/fixtures/execute/tw-wait-until-condition-gh-277.sb3
new file mode 100644
index 00000000..a170d42f
Binary files /dev/null and b/test/fixtures/execute/tw-wait-until-condition-gh-277.sb3 differ
diff --git a/test/snapshot/__snapshots__/tw-wait-until-condition-gh-277.sb3.tw-snapshot b/test/snapshot/__snapshots__/tw-wait-until-condition-gh-277.sb3.tw-snapshot
new file mode 100644
index 00000000..43123670
--- /dev/null
+++ b/test/snapshot/__snapshots__/tw-wait-until-condition-gh-277.sb3.tw-snapshot
@@ -0,0 +1,34 @@
+// TW Snapshot
+// Input SHA-256: 2422e407892596fbf410e032196131f9bae718563fd80b1ff32cf972859c034b
+
+// Sprite1 script
+(function factoryXYZ(thread) { const target = thread.target; const runtime = target.runtime; const stage = runtime.getTargetForStage();
+const b0 = runtime.getOpcodeFunction("looks_say");
+const b1 = stage.variables["`jEk@4|i[#Fk?(8x)AV.-my variable"];
+return function* genXYZ () {
+yield* executeInCompatibilityLayer({"MESSAGE":"plan 0",}, b0, false, false, "e", null);
+startHats("event_whenbroadcastreceived", { BROADCAST_OPTION: "message1" });
+b1.value = "bwah";
+while (!(("" + b1.value).toLowerCase() === "bleh".toLowerCase())) {
+yield;
+}
+yield* executeInCompatibilityLayer({"MESSAGE":"end",}, b0, false, false, "h", null);
+retire(); return;
+}; })
+
+// Sprite1 script
+(function factoryXYZ(thread) { const target = thread.target; const runtime = target.runtime; const stage = runtime.getTargetForStage();
+const b0 = stage.variables["`jEk@4|i[#Fk?(8x)AV.-my variable"];
+return function* genXYZ () {
+b0.value = (1 + 2);
+thread.timer = timer();
+var a0 = Math.max(0, 1000 * 0);
+runtime.requestRedraw();
+yield;
+while (thread.timer.timeElapsed() < a0) {
+yield;
+}
+thread.timer = null;
+b0.value = "bleh";
+retire(); return;
+}; })
diff --git a/test/snapshot/__snapshots__/warp-timer/tw-wait-until-condition-gh-277.sb3.tw-snapshot b/test/snapshot/__snapshots__/warp-timer/tw-wait-until-condition-gh-277.sb3.tw-snapshot
new file mode 100644
index 00000000..43123670
--- /dev/null
+++ b/test/snapshot/__snapshots__/warp-timer/tw-wait-until-condition-gh-277.sb3.tw-snapshot
@@ -0,0 +1,34 @@
+// TW Snapshot
+// Input SHA-256: 2422e407892596fbf410e032196131f9bae718563fd80b1ff32cf972859c034b
+
+// Sprite1 script
+(function factoryXYZ(thread) { const target = thread.target; const runtime = target.runtime; const stage = runtime.getTargetForStage();
+const b0 = runtime.getOpcodeFunction("looks_say");
+const b1 = stage.variables["`jEk@4|i[#Fk?(8x)AV.-my variable"];
+return function* genXYZ () {
+yield* executeInCompatibilityLayer({"MESSAGE":"plan 0",}, b0, false, false, "e", null);
+startHats("event_whenbroadcastreceived", { BROADCAST_OPTION: "message1" });
+b1.value = "bwah";
+while (!(("" + b1.value).toLowerCase() === "bleh".toLowerCase())) {
+yield;
+}
+yield* executeInCompatibilityLayer({"MESSAGE":"end",}, b0, false, false, "h", null);
+retire(); return;
+}; })
+
+// Sprite1 script
+(function factoryXYZ(thread) { const target = thread.target; const runtime = target.runtime; const stage = runtime.getTargetForStage();
+const b0 = stage.variables["`jEk@4|i[#Fk?(8x)AV.-my variable"];
+return function* genXYZ () {
+b0.value = (1 + 2);
+thread.timer = timer();
+var a0 = Math.max(0, 1000 * 0);
+runtime.requestRedraw();
+yield;
+while (thread.timer.timeElapsed() < a0) {
+yield;
+}
+thread.timer = null;
+b0.value = "bleh";
+retire(); return;
+}; })