diff --git a/src/AFQMC/Memory/device_pointers.hpp b/src/AFQMC/Memory/device_pointers.hpp
index 9dc1a5154c..d821edfafa 100644
--- a/src/AFQMC/Memory/device_pointers.hpp
+++ b/src/AFQMC/Memory/device_pointers.hpp
@@ -336,6 +336,7 @@ struct device_pointer : base_device_pointer
   auto operator+(std::ptrdiff_t n) const { return device_pointer{impl_ + n}; }
   auto operator-(std::ptrdiff_t n) const { return device_pointer{impl_ - n}; }
   std::ptrdiff_t operator-(device_pointer other) const { return std::ptrdiff_t(impl_ - other.impl_); }
+  bool operator<(device_pointer const& other) const { return impl_ < other.impl_; }
   operator device_pointer<T const>() const { return device_pointer<T const>{impl_}; }
   operator device_pointer<void const>() const { return device_pointer<void const>{impl_}; }
   device_pointer& operator++()