diff --git a/.changeset/query-devtools-onclose-setter-type.md b/.changeset/query-devtools-onclose-setter-type.md
new file mode 100644
index 00000000000..1e615ae3b67
--- /dev/null
+++ b/.changeset/query-devtools-onclose-setter-type.md
@@ -0,0 +1,5 @@
+---
+'@tanstack/query-devtools': patch
+---
+
+Update the devtools panel `setOnClose` callback type to return `void`.
diff --git a/packages/query-devtools/src/TanstackQueryDevtoolsPanel.tsx b/packages/query-devtools/src/TanstackQueryDevtoolsPanel.tsx
index 6294a6de659..42ee5631961 100644
--- a/packages/query-devtools/src/TanstackQueryDevtoolsPanel.tsx
+++ b/packages/query-devtools/src/TanstackQueryDevtoolsPanel.tsx
@@ -34,7 +34,7 @@ class TanstackQueryDevtoolsPanel {
   #initialIsOpen: Signal<boolean | undefined>
   #errorTypes: Signal<Array<DevtoolsErrorType> | undefined>
   #hideDisabledQueries: Signal<boolean | undefined>
-  #onClose: Signal<(() => unknown) | undefined>
+  #onClose: Signal<(() => void) | undefined>
   #Component: DevtoolsComponentType | undefined
   #theme: Signal<Theme | undefined>
   #dispose?: () => void
@@ -90,7 +90,7 @@ class TanstackQueryDevtoolsPanel {
     this.#client[1](client)
   }
 
-  setOnClose(onClose: () => unknown) {
+  setOnClose(onClose: () => void) {
     this.#onClose[1](() => onClose)
   }