diff --git a/include/blt/std/ranges.h b/include/blt/std/ranges.h
index b45601f..496e139 100644
--- a/include/blt/std/ranges.h
+++ b/include/blt/std/ranges.h
@@ -291,66 +291,66 @@ namespace blt
             constexpr span() noexcept: size_(0), data_(nullptr)
             {}
             
-            template<class It, std::enable_if_t<extent != dynamic_extent, bool> = true>
+            template<class It, std::size_t SIZE, typename std::enable_if_t<extent != dynamic_extent && SIZE == extent, bool> = true>
             constexpr explicit span(It first, size_type count): size_(count), data_(&*first)
             {}
             
-            template<class It, std::enable_if_t<extent == dynamic_extent, bool> = true>
+            template<class It, std::size_t SIZE, typename std::enable_if_t<extent == dynamic_extent && SIZE == extent, bool> = true>
             constexpr span(It first, size_type count): size_(count), data_(&*first)
             {}
             
-            template<class It, class End, std::enable_if_t<extent != dynamic_extent, bool> = true>
+            template<class It, class End, std::size_t SIZE, typename std::enable_if_t<extent != dynamic_extent && SIZE == extent, bool> = true>
             constexpr explicit span(It first, End last): size_(&*last - &*first), data_(&*first)
             {}
             
-            template<class It, class End, std::enable_if_t<extent == dynamic_extent, bool> = true>
+            template<class It, class End, std::size_t SIZE, typename std::enable_if_t<extent == dynamic_extent && SIZE == extent, bool> = true>
             constexpr span(It first, End last): size_(&*last - &*first), data_(&*first)
             {}
             
-            template<std::size_t N, std::enable_if_t<(N == dynamic_extent || N == extent) &&
+            template<std::size_t N, typename std::enable_if_t<(N == dynamic_extent || N == extent) &&
                                                      (std::is_convertible_v<std::remove_pointer_t<decltype(
                                                      std::data(std::declval<T(&)[N]>()))>(*)[], T(*)[]>), bool> = true>
             constexpr span(element_type (& arr)[N]) noexcept: size_{N}, data_{arr}
             {}
             
-            template<class U, std::size_t N, std::enable_if_t<(N == dynamic_extent || N == extent) &&
+            template<class U, std::size_t N, typename std::enable_if_t<(N == dynamic_extent || N == extent) &&
                                                               (std::is_convertible_v<std::remove_pointer_t<decltype(
                                                               std::data(std::declval<T(&)[N]>()))>(*)[], T(*)[]>), bool> = true>
             constexpr span(std::array<U, N>& arr) noexcept: size_(N), data_{arr.data()}
             {}
             
-            template<class U, std::size_t N, std::enable_if_t<(N == dynamic_extent || N == extent) &&
+            template<class U, std::size_t N, typename std::enable_if_t<(N == dynamic_extent || N == extent) &&
                                                               (std::is_convertible_v<std::remove_pointer_t<decltype(
                                                               std::data(std::declval<T(&)[N]>()))>(*)[], T(*)[]>), bool> = true>
             constexpr span(const std::array<U, N>& arr) noexcept: size_(N), data_{arr.data()}
             {}
             
-            template<class R, class RCV = std::remove_cv_t<std::remove_reference_t<R>>, std::enable_if_t<
+            template<class R, class RCV = std::remove_cv_t<std::remove_reference_t<R>>, typename std::enable_if_t<
                     extent != dynamic_extent && span_detail::is_cont_v<RCV> &&
                     std::is_convertible_v<std::remove_pointer_t<decltype(std::data(std::declval<R>()))>(*)[], T(*)[]>, bool> = true>
             explicit constexpr span(R&& range): size_(std::size(range)), data_(std::data(range))
             {}
             
-            template<class R, class RCV = std::remove_cv_t<std::remove_reference_t<R>>, std::enable_if_t<
+            template<class R, class RCV = std::remove_cv_t<std::remove_reference_t<R>>, typename std::enable_if_t<
                     extent == dynamic_extent && span_detail::is_cont_v<RCV> &&
                     std::is_convertible_v<std::remove_pointer_t<decltype(std::data(std::declval<R>()))>(*)[], T(*)[]>, bool> = true>
             constexpr span(R&& range): size_(std::size(range)), data_(std::data(range))
             {}
             
-            template<std::enable_if_t<extent != dynamic_extent && std::is_const_v<element_type>, bool> = true>
+            template<size_type SIZE, typename std::enable_if_t<extent != dynamic_extent && SIZE == extent && std::is_const_v<element_type>, bool> = true>
             explicit constexpr span(std::initializer_list<value_type> il) noexcept: size_(il.size()), data_(&il.begin())
             {}
             
-            template<std::enable_if_t<extent == dynamic_extent && std::is_const_v<element_type>, bool> = true>
+            template<size_type SIZE, typename std::enable_if_t<extent == dynamic_extent && SIZE == extent && std::is_const_v<element_type>, bool> = true>
             explicit span(std::initializer_list<value_type> il) noexcept: size_(il.size()), data_(&il.begin())
             {}
             
-            template<class U, std::size_t N, std::enable_if_t<
+            template<class U, std::size_t N, typename std::enable_if_t<
                     extent != dynamic_extent && N == dynamic_extent && std::is_convertible_v<U(*)[], T(*)[]>, bool> = true>
             explicit constexpr span(const span<U, N>& source) noexcept: size_{source.size()}, data_{source.data()}
             {}
             
-            template<class U, std::size_t N, std::enable_if_t<
+            template<class U, std::size_t N, typename std::enable_if_t<
                     !(extent != dynamic_extent && N == dynamic_extent) && std::is_convertible_v<U(*)[], T(*)[]>, bool> = true>
             constexpr span(const span<U, N>& source) noexcept: size_{source.size()}, data_{source.data()}
             {}