diff --git a/include/gsl/gsl_byte b/include/gsl/gsl_byte
index 861446d..1670646 100644
--- a/include/gsl/gsl_byte
+++ b/include/gsl/gsl_byte
@@ -56,6 +56,7 @@
 #else // _MSC_VER
 
 #ifndef GSL_USE_STD_BYTE
+#include <cstddef> /* __cpp_lib_byte */
 // this tests if we are under GCC or Clang with enough -std:c++1z power to get us std::byte
 // also check if libc++ version is sufficient (> 5.0) or libstc++ actually contains std::byte
 #if defined(__cplusplus) && (__cplusplus >= 201703L) && \
@@ -63,7 +64,6 @@
    defined(_LIBCPP_VERSION) && (_LIBCPP_VERSION >= 5000))
 
 #define GSL_USE_STD_BYTE 1
-#include <cstddef>
 
 #else // defined(__cplusplus) && (__cplusplus >= 201703L) &&
       //   (defined(__cpp_lib_byte) && (__cpp_lib_byte >= 201603)  ||
diff --git a/include/gsl/gsl_util b/include/gsl/gsl_util
index 4addde6..0fce689 100644
--- a/include/gsl/gsl_util
+++ b/include/gsl/gsl_util
@@ -37,7 +37,7 @@
 #endif            // _MSC_VER < 1910
 #endif            // _MSC_VER
 
-#if (defined(_MSC_VER) && _MSC_VER < 1910) || (!defined(__clang__) && defined(__GNUC__) && __GUNC__ < 6)
+#if (defined(_MSC_VER) && _MSC_VER < 1910) || (!defined(__clang__) && defined(__GNUC__) && __GNUC__ < 6)
 #define GSL_CONSTEXPR_NARROW 0
 #else
 #define GSL_CONSTEXPR_NARROW 1
diff --git a/include/gsl/span b/include/gsl/span
index b4da532..59bd121 100644
--- a/include/gsl/span
+++ b/include/gsl/span
@@ -141,7 +141,7 @@ namespace details
 
         span_iterator() = default;
 
-        constexpr span_iterator(const Span* span, typename Span::index_type idx) noexcept
+        constexpr span_iterator(const Span* span, difference_type idx) noexcept
             : span_(span), index_(idx)
         {}
 
diff --git a/include/gsl/string_span b/include/gsl/string_span
index 85112e5..37cbe15 100644
--- a/include/gsl/string_span
+++ b/include/gsl/string_span
@@ -20,7 +20,6 @@
 #include <gsl/gsl_assert> // for Ensures, Expects
 #include <gsl/gsl_util>   // for narrow_cast
 #include <gsl/span>       // for operator!=, operator==, dynamic_extent
-#include <gsl/pointers>   // for not_null
 
 #include <algorithm> // for equal, lexicographical_compare
 #include <array>     // for array