diff --git a/packages/core/README.md b/packages/core/README.md
index 85456d3..a83bd73 100644
--- a/packages/core/README.md
+++ b/packages/core/README.md
@@ -119,6 +119,11 @@ bridge state, and mapped into XInput/HID trigger bytes for trigger-like buttons.
 Plain binary presses on trigger-like buttons, such as `press("RT", 0)`, map to a
 full analog pull.
 
+Timed actions reject negative `durationMs` values. A zero duration remains
+persistent where the action API uses zero-duration input, while positive values
+request a timed hold. The requested SDK duration is not a guarantee of how long
+the target game observes the input or how many frames it spans.
+
 Direct D-pad button presses also keep the structured D-pad state synchronized:
 
 ```ts
diff --git a/packages/core/src/__tests__/negative-duration-validation.test.ts b/packages/core/src/__tests__/negative-duration-validation.test.ts
new file mode 100644
index 0000000..13de5b9
--- /dev/null
+++ b/packages/core/src/__tests__/negative-duration-validation.test.ts
@@ -0,0 +1,90 @@
+import { describe, expect, spyOn, test } from "bun:test";
+import { createActionMap, createController, DryRunAdapter } from "../index";
+
+describe("negative action duration validation", () => {
+  test("rejects negative durations before adapter output across command paths", async () => {
+    const adapter = new DryRunAdapter();
+    const controller = await createController({
+      profile: "xbox",
+      adapter,
+      replay: false,
+    });
+    const initialHistoryLength = adapter.history.length;
+    const initialStateHistoryLength = adapter.stateHistory.length;
+    const neutral = spyOn(adapter, "neutral");
+
+    await expect(controller.press("A", -1)).rejects.toThrow(
+      "must not be negative",
+    );
+    await expect(controller.trigger("RT", 1, -1)).rejects.toThrow(
+      "must not be negative",
+    );
+
+    const negativeCommands = [
+      { type: "press", button: "A", durationMs: -1 },
+      { type: "stick", stick: "LEFT", x: 1, y: 0, durationMs: -1 },
+      { type: "trigger", trigger: "RT", value: 1, durationMs: -1 },
+      { type: "dpad", direction: "UP", durationMs: -1 },
+      { type: "combo", buttons: ["A", "B"], durationMs: -1 },
+      { type: "touchpad", pressed: true, durationMs: -1 },
+      { type: "motion", durationMs: -1 },
+    ] as const;
+
+    for (const command of negativeCommands) {
+      await expect(controller.sequence([command])).rejects.toThrow(
+        "must not be negative",
+      );
+    }
+
+    await expect(
+      controller.sequence([
+        { type: "press", button: "A", durationMs: 0 },
+        {
+          type: "sequence",
+          commands: [
+            { type: "trigger", trigger: "RT", value: 1, durationMs: -1 },
+          ],
+        },
+      ]),
+    ).rejects.toThrow("must not be negative");
+
+    const actions = createActionMap(controller, {
+      attack: [{ type: "press", button: "A", durationMs: 50 }],
+    });
+    await expect(actions.run("attack", { durationMs: -1 })).rejects.toThrow(
+      "must not be negative",
+    );
+
+    expect(adapter.history).toHaveLength(initialHistoryLength);
+    expect(adapter.stateHistory).toHaveLength(initialStateHistoryLength);
+    expect(neutral).not.toHaveBeenCalled();
+    neutral.mockRestore();
+    await controller.disconnect();
+  });
+
+  test("keeps zero-duration input persistent and positive durations timed", async () => {
+    const adapter = new DryRunAdapter();
+    const controller = await createController({
+      profile: "xbox",
+      adapter,
+      replay: false,
+    });
+
+    await controller.press("A", 0);
+    expect(controller.getState().buttons.A).toBe(true);
+
+    await controller.trigger("RT", 0.5, 0);
+    expect(controller.getState().analogButtons.RT).toBe(0.5);
+
+    await controller.trigger("RT", 1, 1);
+    expect(controller.getState().analogButtons.RT).toBe(0);
+    expect(adapter.history.map((entry) => entry.command.type)).toEqual([
+      "press",
+      "trigger",
+      "trigger",
+      "trigger",
+    ]);
+
+    await controller.disconnect();
+  });
+});
diff --git a/packages/core/src/runtime.ts b/packages/core/src/runtime.ts
index 1042fa4..2c29b8a 100644
--- a/packages/core/src/runtime.ts
+++ b/packages/core/src/runtime.ts
@@ -73,6 +73,7 @@ export class ControllerRuntime {
     context: CommandContext = {},
     signal?: AbortSignal,
   ): Promise<void> {
+    this.safety.assertNonNegativeDurations(command);
     const timedPressSignal = isPositiveTimedPress(command) ? signal : undefined;
     if (timedPressSignal?.aborted) {
       throw new TimedPressAbortError({
diff --git a/packages/core/src/safety.ts b/packages/core/src/safety.ts
index ceed16c..6f85f3c 100644
--- a/packages/core/src/safety.ts
+++ b/packages/core/src/safety.ts
@@ -58,12 +58,31 @@ export class SafetyGuard {
   }
 
   assert(command: ControllerCommand): void {
+    this.assertNonNegativeDurations(command);
     this.assertRateLimit();
     this.assertDurations(command);
     this.assertDisabledControls(command);
     this.assertInputLoop(command);
   }
 
+  assertNonNegativeDurations(command: ControllerCommand): void {
+    if (
+      "durationMs" in command &&
+      command.durationMs !== undefined &&
+      command.durationMs < 0
+    ) {
+      throw new SafetyError(
+        `Action duration ${command.durationMs}ms must not be negative`,
+      );
+    }
+
+    if (command.type === "sequence") {
+      for (const child of command.commands) {
+        this.assertNonNegativeDurations(child);
+      }
+    }
+  }
+
   private assertRateLimit(): void {
     const now = Date.now();
     this.commandTimestamps.push(now);
@@ -88,7 +107,7 @@ export class SafetyGuard {
       (command.type === "press" ||
         command.type === "combo" ||
         command.type === "dpad") &&
-      command.durationMs
+      command.durationMs !== undefined
     ) {
       if (command.durationMs > this.config.maxButtonHoldMs) {
         throw new SafetyError(
@@ -101,7 +120,7 @@ export class SafetyGuard {
       (command.type === "stick" ||
         command.type === "touchpad" ||
         command.type === "motion") &&
-      command.durationMs
+      command.durationMs !== undefined
     ) {
       if (command.durationMs > this.config.maxStickHoldMs) {
         throw new SafetyError(