From 552c46f7b114466c760bb63fba4ae1e4842f5f53 Mon Sep 17 00:00:00 2001
From: Peter Hawkins <phawkins@google.com>
Date: Mon, 16 Feb 2026 19:05:28 +0100
Subject: [PATCH] BUG: Fix weak hash function in np.isin(). (#30840)

---
 numpy/_core/src/multiarray/unique.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/numpy/_core/src/multiarray/unique.cpp b/numpy/_core/src/multiarray/unique.cpp
index 675e0226d14f..a8b897446182 100644
--- a/numpy/_core/src/multiarray/unique.cpp
+++ b/numpy/_core/src/multiarray/unique.cpp
@@ -63,7 +63,7 @@ empty_array_like(PyArrayObject *arr, npy_intp length)
 
 template <typename T>
 size_t hash_integer(const T *value, npy_bool equal_nan) {
-    return std::hash<T>{}(*value);
+    return npy_fnv1a(reinterpret_cast<const unsigned char*>(value), sizeof(T));
 }
 
 template <typename S, typename T, S (*real)(T), S (*imag)(T)>