diff --git a/include/gsl/gsl b/include/gsl/gsl
index 6415d48..55862eb 100644
--- a/include/gsl/gsl
+++ b/include/gsl/gsl
@@ -21,7 +21,6 @@
 #include <gsl/gsl_assert>    // Ensures/Expects
 #include <gsl/gsl_byte>      // byte
 #include <gsl/gsl_util>      // finally()/narrow()/narrow_cast()...
-#include <gsl/index>         // index
 #include <gsl/multi_span>    // multi_span, strided_span...
 #include <gsl/pointers>      // owner, not_null
 #include <gsl/span>          // span
diff --git a/include/gsl/gsl_util b/include/gsl/gsl_util
index eee63e7..58e0a37 100644
--- a/include/gsl/gsl_util
+++ b/include/gsl/gsl_util
@@ -43,6 +43,9 @@ namespace gsl
 // GSL.util: utilities
 //
 
+// index type for all container indexes/subscripts/sizes
+using index = std::ptrdiff_t;
+
 // final_action allows you to ensure something gets run at the end of a scope
 template <class F>
 class final_action
diff --git a/include/gsl/index b/include/gsl/index
deleted file mode 100644
index 176860c..0000000
--- a/include/gsl/index
+++ /dev/null
@@ -1,27 +0,0 @@
-///////////////////////////////////////////////////////////////////////////////
-//
-// 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.
-//
-///////////////////////////////////////////////////////////////////////////////
-
-#ifndef GSL_INDEX_H
-#define GSL_INDEX_H
-
-#include <cstddef> // for ptrdiff_t
-
-namespace gsl
-{
-using index = std::ptrdiff_t;
-}
-
-#endif // GSL_INDEX_H
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 544d1cc..86ce5a4 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -101,4 +101,3 @@ add_gsl_test(utils_tests)
 add_gsl_test(owner_tests)
 add_gsl_test(byte_tests)
 add_gsl_test(algorithm_tests)
-add_gsl_test(index_test)
diff --git a/tests/index_test.cpp b/tests/index_test.cpp
deleted file mode 100644
index 761e70f..0000000
--- a/tests/index_test.cpp
+++ /dev/null
@@ -1,26 +0,0 @@
-///////////////////////////////////////////////////////////////////////////////
-//
-// 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.
-//
-///////////////////////////////////////////////////////////////////////////////
-
-#include <catch/catch.hpp>
-#include <type_traits> // for is_same
-
-#include <gsl/index> // for index
-
-TEST_CASE("sanity check for gsl::index typedef")
-{
-    static_assert(std::is_same<gsl::index, std::ptrdiff_t>::value,
-                  "gsl::index represents wrong arithmetic type");
-}
diff --git a/tests/utils_tests.cpp b/tests/utils_tests.cpp
index 610efbf..587b0a1 100644
--- a/tests/utils_tests.cpp
+++ b/tests/utils_tests.cpp
@@ -18,13 +18,20 @@
 
 #include <gsl/gsl_util> // for narrow, finally, narrow_cast, narrowing_e...
 
-#include <algorithm>  // for move
-#include <functional> // for reference_wrapper, _Bind_helper<>::type
-#include <limits>     // for numeric_limits
-#include <stdint.h>   // for uint32_t, int32_t
+#include <algorithm>   // for move
+#include <functional>  // for reference_wrapper, _Bind_helper<>::type
+#include <limits>      // for numeric_limits
+#include <stdint.h>    // for uint32_t, int32_t
+#include <type_traits> // for is_same
 
 using namespace gsl;
 
+TEST_CASE("sanity check for gsl::index typedef")
+{
+    static_assert(std::is_same<gsl::index, std::ptrdiff_t>::value,
+                  "gsl::index represents wrong arithmetic type");
+}
+
 void f(int& i) { i += 1; }
 
 TEST_CASE("finally_lambda")