diff --git a/include/gsl/gsl b/include/gsl/gsl
index 4cb03c5..4f69bbf 100644
--- a/include/gsl/gsl
+++ b/include/gsl/gsl
@@ -24,167 +24,6 @@
 #include <gsl/multi_span>  // multi_span, strided_span...
 #include <gsl/span>        // span
 #include <gsl/string_span> // zstring, string_span, zstring_builder...
-
-#include <iostream>
-#include <memory>
-#include <type_traits>
-
-#if defined(_MSC_VER) && _MSC_VER < 1910
-#pragma push_macro("constexpr")
-#define constexpr /*constexpr*/
-
-#endif                          // defined(_MSC_VER) && _MSC_VER < 1910
-
-namespace gsl
-{
-
-//
-// GSL.owner: ownership pointers
-//
-using std::unique_ptr;
-using std::shared_ptr;
-
-//
-// owner
-//
-// owner<T> is designed as a bridge for code that must deal directly with owning pointers for some reason
-//
-// T must be a pointer type
-// - disallow construction from any type other than pointer type
-//
-template <class T, class = std::enable_if_t<std::is_pointer<T>::value>>
-using owner = T;
-
-//
-// not_null
-//
-// Restricts a pointer or smart pointer to only hold non-null values.
-//
-// Has zero size overhead over T.
-//
-// If T is a pointer (i.e. T == U*) then
-// - allow construction from U*
-// - disallow construction from nullptr_t
-// - disallow default construction
-// - ensure construction from null U* fails
-// - allow implicit conversion to U*
-//
-template <class T>
-class not_null
-{
-public:
-    static_assert(std::is_assignable<T&, std::nullptr_t>::value, "T cannot be assigned nullptr.");
-
-    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
-    constexpr not_null(U&& u) : ptr_(std::forward<U>(u))
-    {
-        Expects(ptr_ != nullptr);
-    }
-
-    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
-    constexpr not_null(const not_null<U>& other) : not_null(other.get())
-    {
-    }
-
-    not_null(const not_null& other) = default;
-    not_null& operator=(const not_null& other) = default;
-
-    constexpr T get() const
-    {
-        Ensures(ptr_ != nullptr);
-        return ptr_;
-    }
-
-    constexpr operator T() const { return get(); }
-    constexpr T operator->() const { return get(); }
-    constexpr decltype(auto) operator*() const { return *get(); } 
-
-    // prevents compilation when someone attempts to assign a null pointer constant
-    not_null(std::nullptr_t) = delete;
-    not_null& operator=(std::nullptr_t) = delete;
-
-    // unwanted operators...pointers only point to single objects!
-    not_null& operator++() = delete;
-    not_null& operator--() = delete;
-    not_null operator++(int) = delete;
-    not_null operator--(int) = delete;
-    not_null& operator+=(std::ptrdiff_t) = delete;
-    not_null& operator-=(std::ptrdiff_t) = delete;
-    void operator[](std::ptrdiff_t) const = delete;
-
-private:
-    T ptr_;
-};
-
-template <class T>
-std::ostream& operator<<(std::ostream& os, const not_null<T>& val)
-{
-    os << val.get();
-    return os;
-}
-
-template <class T, class U>
-auto operator==(const not_null<T>& lhs, const not_null<U>& rhs) -> decltype(lhs.get() == rhs.get())
-{
-    return lhs.get() == rhs.get();
-}
-
-template <class T, class U>
-auto operator!=(const not_null<T>& lhs, const not_null<U>& rhs) -> decltype(lhs.get() != rhs.get())
-{
-    return lhs.get() != rhs.get();
-}
-
-template <class T, class U>
-auto operator<(const not_null<T>& lhs, const not_null<U>& rhs) -> decltype(lhs.get() < rhs.get())
-{
-    return lhs.get() < rhs.get();
-}
-
-template <class T, class U>
-auto operator<=(const not_null<T>& lhs, const not_null<U>& rhs) -> decltype(lhs.get() <= rhs.get())
-{
-    return lhs.get() <= rhs.get();
-}
-
-template <class T, class U>
-auto operator>(const not_null<T>& lhs, const not_null<U>& rhs) -> decltype(lhs.get() > rhs.get())
-{
-    return lhs.get() > rhs.get();
-}
-
-template <class T, class U>
-auto operator>=(const not_null<T>& lhs, const not_null<U>& rhs) -> decltype(lhs.get() >= rhs.get())
-{
-    return lhs.get() >= rhs.get();
-}
-
-// more unwanted operators
-template <class T, class U>
-std::ptrdiff_t operator-(const not_null<T>&, const not_null<U>&) = delete;
-template <class T>
-not_null<T> operator-(const not_null<T>&, std::ptrdiff_t) = delete;
-template <class T>
-not_null<T> operator+(const not_null<T>&, std::ptrdiff_t) = delete;
-template <class T>
-not_null<T> operator+(std::ptrdiff_t, const not_null<T>&) = delete;
-
-} // namespace gsl
-
-namespace std
-{
-template <class T>
-struct hash<gsl::not_null<T>>
-{
-    std::size_t operator()(const gsl::not_null<T>& value) const { return hash<T>{}(value); }
-};
-
-} // namespace std
-
-#if defined(_MSC_VER) && _MSC_VER < 1910
-#undef constexpr
-#pragma pop_macro("constexpr")
-
-#endif // defined(_MSC_VER) && _MSC_VER < 1910
+#include <gsl/pointers>    // owner, not_null
 
 #endif // GSL_GSL_H
diff --git a/include/gsl/pointers b/include/gsl/pointers
new file mode 100644
index 0000000..a02d3a9
--- /dev/null
+++ b/include/gsl/pointers
@@ -0,0 +1,186 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+//
+// This code is licensed under the MIT License (MIT).
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#pragma once
+
+#ifndef GSL_POINTERS_H
+#define GSL_POINTERS_H
+
+#include <gsl/gsl_assert>
+
+#include <iostream>
+#include <memory>
+#include <type_traits>
+
+#if defined(_MSC_VER) && _MSC_VER < 1910
+#pragma push_macro("constexpr")
+#define constexpr /*constexpr*/
+
+#endif                          // defined(_MSC_VER) && _MSC_VER < 1910
+
+namespace gsl
+{
+
+//
+// GSL.owner: ownership pointers
+//
+using std::unique_ptr;
+using std::shared_ptr;
+
+//
+// owner
+//
+// owner<T> is designed as a bridge for code that must deal directly with owning pointers for some reason
+//
+// T must be a pointer type
+// - disallow construction from any type other than pointer type
+//
+template <class T, class = std::enable_if_t<std::is_pointer<T>::value>>
+using owner = T;
+
+//
+// not_null
+//
+// Restricts a pointer or smart pointer to only hold non-null values.
+//
+// Has zero size overhead over T.
+//
+// If T is a pointer (i.e. T == U*) then
+// - allow construction from U*
+// - disallow construction from nullptr_t
+// - disallow default construction
+// - ensure construction from null U* fails
+// - allow implicit conversion to U*
+//
+template <class T>
+class not_null
+{
+public:
+    static_assert(std::is_assignable<T&, std::nullptr_t>::value, "T cannot be assigned nullptr.");
+
+    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
+    constexpr not_null(U&& u) : ptr_(std::forward<U>(u))
+    {
+        Expects(ptr_ != nullptr);
+    }
+
+    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
+    constexpr not_null(const not_null<U>& other) : not_null(other.get())
+    {
+    }
+
+    not_null(const not_null& other) = default;
+    not_null& operator=(const not_null& other) = default;
+
+    constexpr T get() const
+    {
+        Ensures(ptr_ != nullptr);
+        return ptr_;
+    }
+
+    constexpr operator T() const { return get(); }
+    constexpr T operator->() const { return get(); }
+    constexpr decltype(auto) operator*() const { return *get(); } 
+
+    // prevents compilation when someone attempts to assign a null pointer constant
+    not_null(std::nullptr_t) = delete;
+    not_null& operator=(std::nullptr_t) = delete;
+
+    // unwanted operators...pointers only point to single objects!
+    not_null& operator++() = delete;
+    not_null& operator--() = delete;
+    not_null operator++(int) = delete;
+    not_null operator--(int) = delete;
+    not_null& operator+=(std::ptrdiff_t) = delete;
+    not_null& operator-=(std::ptrdiff_t) = delete;
+    void operator[](std::ptrdiff_t) const = delete;
+
+private:
+    T ptr_;
+};
+
+template <class T>
+std::ostream& operator<<(std::ostream& os, const not_null<T>& val)
+{
+    os << val.get();
+    return os;
+}
+
+template <class T, class U>
+auto operator==(const not_null<T>& lhs, const not_null<U>& rhs) -> decltype(lhs.get() == rhs.get())
+{
+    return lhs.get() == rhs.get();
+}
+
+template <class T, class U>
+auto operator!=(const not_null<T>& lhs, const not_null<U>& rhs) -> decltype(lhs.get() != rhs.get())
+{
+    return lhs.get() != rhs.get();
+}
+
+template <class T, class U>
+auto operator<(const not_null<T>& lhs, const not_null<U>& rhs) -> decltype(lhs.get() < rhs.get())
+{
+    return lhs.get() < rhs.get();
+}
+
+template <class T, class U>
+auto operator<=(const not_null<T>& lhs, const not_null<U>& rhs) -> decltype(lhs.get() <= rhs.get())
+{
+    return lhs.get() <= rhs.get();
+}
+
+template <class T, class U>
+auto operator>(const not_null<T>& lhs, const not_null<U>& rhs) -> decltype(lhs.get() > rhs.get())
+{
+    return lhs.get() > rhs.get();
+}
+
+template <class T, class U>
+auto operator>=(const not_null<T>& lhs, const not_null<U>& rhs) -> decltype(lhs.get() >= rhs.get())
+{
+    return lhs.get() >= rhs.get();
+}
+
+// more unwanted operators
+template <class T, class U>
+std::ptrdiff_t operator-(const not_null<T>&, const not_null<U>&) = delete;
+template <class T>
+not_null<T> operator-(const not_null<T>&, std::ptrdiff_t) = delete;
+template <class T>
+not_null<T> operator+(const not_null<T>&, std::ptrdiff_t) = delete;
+template <class T>
+not_null<T> operator+(std::ptrdiff_t, const not_null<T>&) = delete;
+
+} // namespace gsl
+
+namespace std
+{
+template <class T>
+struct hash<gsl::not_null<T>>
+{
+    std::size_t operator()(const gsl::not_null<T>& value) const { return hash<T>{}(value); }
+};
+
+} // namespace std
+
+#if defined(_MSC_VER) && _MSC_VER < 1910
+#undef constexpr
+#pragma pop_macro("constexpr")
+
+#endif // defined(_MSC_VER) && _MSC_VER < 1910
+
+#endif // GSL_POINTERS_H
diff --git a/tests/notnull_tests.cpp b/tests/notnull_tests.cpp
index 62f1e57..6111553 100644
--- a/tests/notnull_tests.cpp
+++ b/tests/notnull_tests.cpp
@@ -16,7 +16,7 @@
 
 #include <catch/catch.hpp>
 
-#include <gsl/gsl>
+#include <gsl/pointers>
 
 #include <memory>
 #include <string>
diff --git a/tests/owner_tests.cpp b/tests/owner_tests.cpp
index 9885a68..dbc8d16 100644
--- a/tests/owner_tests.cpp
+++ b/tests/owner_tests.cpp
@@ -16,10 +16,9 @@
 
 #include <catch/catch.hpp>
 
-#include <gsl/gsl>
+#include <gsl/pointers>
 
 #include <functional>
-
 #include <memory>
 
 using namespace gsl;