diff --git a/denops/ddc/app.ts b/denops/ddc/app.ts
index 5090bd9..4dbb58b 100644
--- a/denops/ddc/app.ts
+++ b/denops/ddc/app.ts
@@ -34,6 +34,7 @@ export const main: Entrypoint = (denops: Denops) => {
   const cbContext = createCallbackContext();
   const lock = new Lock(0);
   let queuedEvent: DdcEvent | null = null;
+  const autoCompleteTimers = new Map<number, number>();
 
   const setAlias = (extType: DdcExtType, alias: string, base: string) => {
     loader.registerAlias(extType, alias, base);
@@ -260,6 +261,11 @@ export const main: Entrypoint = (denops: Denops) => {
     async onEvent(arg1: unknown): Promise<void> {
       queuedEvent = ensure(arg1, is.String) as DdcEvent;
 
+      // Revoke immediately to cancel any pending callback waits from the
+      // previous event processing, allowing it to fail fast and release the
+      // lock sooner.
+      cbContext.revoke();
+
       // NOTE: must be locked
       await lock.lock(async () => {
         while (queuedEvent !== null) {
@@ -385,15 +391,29 @@ export const main: Entrypoint = (denops: Denops) => {
 
     // Check auto complete delay.
     if (options.autoCompleteDelay > 0) {
-      // Cancel previous completion
-      await ddc.cancelCompletion(denops, context, options);
-
-      await new Promise((resolve) =>
-        setTimeout(
-          resolve,
-          options.autoCompleteDelay,
-        )
-      );
+      // Cancel previous timer for this buffer (debounce)
+      clearTimeout(autoCompleteTimers.get(context.bufNr));
+
+      // Set a new per-buffer debounce timer.  When it fires, cancel the
+      // previous completion once and then run doCompletion, avoiding
+      // repeated cancelCompletion/hide calls during rapid input.
+      const timerId = setTimeout(() => {
+        autoCompleteTimers.delete(context.bufNr);
+
+        lock.lock(async () => {
+          await ddc.cancelCompletion(denops, context, options);
+
+          if (options.hideOnEvents || event === "Update") {
+            // Hide the current completion
+            await ddc.hide(denops, context, options);
+          }
+
+          await ddc.doCompletion(denops, context, cbContext, options);
+        });
+      }, options.autoCompleteDelay);
+
+      autoCompleteTimers.set(context.bufNr, timerId);
+      return;
     }
 
     if (options.hideOnEvents || event === "Update") {
diff --git a/denops/ddc/context.ts b/denops/ddc/context.ts
index c656952..f6d473d 100644
--- a/denops/ddc/context.ts
+++ b/denops/ddc/context.ts
@@ -420,6 +420,7 @@ export class ContextBuilderImpl implements ContextBuilder {
     }
 
     const context = {
+      bufNr: world.bufnr,
       cursor: world.cursor,
       event: event,
       filetype: world.filetype,
diff --git a/denops/ddc/types.ts b/denops/ddc/types.ts
index 5496e28..e62600a 100644
--- a/denops/ddc/types.ts
+++ b/denops/ddc/types.ts
@@ -16,6 +16,7 @@ export type SourceName = string;
 export type FilterName = string;
 
 export type Context = {
+  bufNr: number;
   cursor: (number | undefined)[];
   event: DdcEvent;
   filetype: string;