diff --git a/include/gsl/span b/include/gsl/span
index 5f66c6c..ef7580c 100644
--- a/include/gsl/span
+++ b/include/gsl/span
@@ -333,7 +333,7 @@ namespace details
     public:
         using index_type = std::size_t;
 
-        static_assert(Ext >= 0, "A fixed-size span must be >= 0 in size.");
+        static_assert(Ext != dynamic_extent, "A fixed-size span must be >= 0 in size.");
 
         constexpr extent_type() noexcept {}
 
@@ -417,7 +417,7 @@ public:
     constexpr span(pointer ptr, index_type count) noexcept : storage_(ptr, count) {}
 
     constexpr span(pointer firstElem, pointer lastElem) noexcept
-        : storage_(firstElem, std::distance(firstElem, lastElem))
+        : storage_(firstElem, static_cast<std::size_t>(std::distance(firstElem, lastElem)))
     {}
 
     template <std::size_t N>
@@ -536,7 +536,7 @@ public:
     GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
     constexpr reference operator[](index_type idx) const noexcept
     {
-        Expects(CheckRange(idx, storage_.size()));
+        Expects(idx < size());
         return data()[idx];
     }
 
@@ -594,32 +594,6 @@ public:
 #endif // _MSC_VER
 
 private:
-    static constexpr bool CheckRange(index_type idx, index_type size) noexcept
-    {
-        // Optimization:
-        //
-        // idx >= 0 && idx < size
-        // =>
-        // static_cast<size_t>(idx) < static_cast<size_t>(size)
-        //
-        // because size >=0 by span construction, and negative idx will
-        // wrap around to a value always greater than size when casted.
-
-        // check if we have enough space to wrap around
-#if defined(__cpp_if_constexpr)
-        if constexpr (sizeof(index_type) <= sizeof(size_t))
-#else
-        if (sizeof(index_type) <= sizeof(size_t))
-#endif
-        {
-            return narrow_cast<size_t>(idx) < narrow_cast<size_t>(size);
-        }
-        else
-        {
-            return idx < size;
-        }
-    }
-
     // Needed to remove unnecessary null check in subspans
     struct KnownNotNull
     {