diff --git a/cruft/util/coord/base.hpp b/cruft/util/coord/base.hpp
index e3c23551..98dc1e10 100644
--- a/cruft/util/coord/base.hpp
+++ b/cruft/util/coord/base.hpp
@@ -75,11 +75,15 @@ namespace cruft::coord {
         }
 
         // element accessors
-        constexpr T& operator[] (size_t i)& noexcept { return this->data[i]; }
-        constexpr T& operator[] (int i)& noexcept { return this->data[i]; }
+        template <typename IdxT>
+        constexpr T&
+        operator[] (IdxT i)& noexcept
+        { return this->data[i]; }
 
-        constexpr const T& operator[] (size_t i) const& noexcept { return this->data[i]; }
-        constexpr const T& operator[] (int i) const& noexcept { return this->data[i]; }
+        template <typename IdxT>
+        constexpr const T&
+        operator[] (IdxT i) const& noexcept
+        { return this->data[i]; }
 
         auto cbegin (void) const { return std::cbegin (this->data); }
         auto cend   (void) const { return std::cend   (this->data); }