diff --git a/.changeset/fix-timer-id-zero-falsy-check.md b/.changeset/fix-timer-id-zero-falsy-check.md
new file mode 100644
index 00000000000..7bec3cdab1c
--- /dev/null
+++ b/.changeset/fix-timer-id-zero-falsy-check.md
@@ -0,0 +1,5 @@
+---
+'@tanstack/query-core': patch
+---
+
+fix(query-core): use explicit `undefined` check for timer IDs so that custom `TimeoutProvider`s returning `0` as a valid timer ID are properly cleared
diff --git a/packages/query-core/src/queryObserver.ts b/packages/query-core/src/queryObserver.ts
index a290c700b58..fa950bcfff3 100644
--- a/packages/query-core/src/queryObserver.ts
+++ b/packages/query-core/src/queryObserver.ts
@@ -417,14 +417,14 @@ export class QueryObserver<
   }
 
   #clearStaleTimeout(): void {
-    if (this.#staleTimeoutId) {
+    if (this.#staleTimeoutId !== undefined) {
       timeoutManager.clearTimeout(this.#staleTimeoutId)
       this.#staleTimeoutId = undefined
     }
   }
 
   #clearRefetchInterval(): void {
-    if (this.#refetchIntervalId) {
+    if (this.#refetchIntervalId !== undefined) {
       timeoutManager.clearInterval(this.#refetchIntervalId)
       this.#refetchIntervalId = undefined
     }
diff --git a/packages/query-core/src/removable.ts b/packages/query-core/src/removable.ts
index 68545f74383..62e524219ca 100644
--- a/packages/query-core/src/removable.ts
+++ b/packages/query-core/src/removable.ts
@@ -30,7 +30,7 @@ export abstract class Removable {
   }
 
   protected clearGcTimeout() {
-    if (this.#gcTimeout) {
+    if (this.#gcTimeout !== undefined) {
       timeoutManager.clearTimeout(this.#gcTimeout)
       this.#gcTimeout = undefined
     }