diff --git a/FFT3DFilter.h b/FFT3DFilter.h
index 3c2dc5c..e0e409e 100644
--- a/FFT3DFilter.h
+++ b/FFT3DFilter.h
@@ -69,7 +69,7 @@ class ThreadLocalPtrPool {
     T* get() noexcept;
 
     ~ThreadLocalPtrPool() noexcept {
-        for (const auto [_, ptr] : pool) {
+        for (const auto &[_, ptr] : pool) {
             Deleter(ptr);
         }
     }