diff --git a/docs/users_guide/use_cases/wide_compatibility.md b/docs/users_guide/use_cases/wide_compatibility.md
index 85dd916d..b8e7d465 100644
--- a/docs/users_guide/use_cases/wide_compatibility.md
+++ b/docs/users_guide/use_cases/wide_compatibility.md
@@ -157,3 +157,23 @@ from additional features provided with the library).
 This macro resolves to either the `std` or `fmt` namespace, depending on the value of
 [MP_UNITS_API_STD_FORMAT](../../getting_started/installation_and_usage.md#MP_UNITS_API_STD_FORMAT)
 CMake option.
+
+### Contracts
+
+The mp-units library internally does contract checking by default. It can be disabled with a Conan
+or CMake option. However, when enabled, it can use either [gsl-lite](https://github.com/gsl-lite/gsl-lite)
+or [ms-gsl](https://github.com/microsoft/GSL). To write a code that is independent from the
+underlying framework, the following preprocessor macros are exposed:
+
+- `MP_UNITS_EXPECTS(expr)`
+- `MP_UNITS_EXPECTS_DEBUG(expr)`
+- `MP_UNITS_ASSERT(expr)`
+- `MP_UNITS_ASSERT_DEBUG(expr)`
+
+Their meaning is consistent with respective [gsl-lite](https://github.com/gsl-lite/gsl-lite?tab=readme-ov-file#contract-checking-configuration-macros).
+
+Also, to include the header files of the underlying framework, the following include should be used:
+
+```cpp
+#include <mp-units/ext/contracts.h>
+```
diff --git a/example/include/validated_type.h b/example/include/validated_type.h
index 9a429e26..a0a7b91c 100644
--- a/example/include/validated_type.h
+++ b/example/include/validated_type.h
@@ -24,6 +24,7 @@
 
 #include <mp-units/bits/hacks.h>
 #include <mp-units/compat_macros.h>
+#include <mp-units/ext/contracts.h>
 #include <compare>  // IWYU pragma: export
 #include <ostream>
 #include <utility>
diff --git a/src/core/CMakeLists.txt b/src/core/CMakeLists.txt
index 5ee3c155..733e3586 100644
--- a/src/core/CMakeLists.txt
+++ b/src/core/CMakeLists.txt
@@ -44,6 +44,7 @@ add_mp_units_module(
             include/mp-units/bits/text_tools.h
             include/mp-units/bits/type_list.h
             include/mp-units/ext/algorithm.h
+            include/mp-units/ext/contracts.h
             include/mp-units/ext/fixed_string.h
             include/mp-units/ext/prime.h
             include/mp-units/ext/type_name.h
diff --git a/src/core/include/mp-units/bits/core_gmf.h b/src/core/include/mp-units/bits/core_gmf.h
index 21d97e8f..08defcae 100644
--- a/src/core/include/mp-units/bits/core_gmf.h
+++ b/src/core/include/mp-units/bits/core_gmf.h
@@ -24,6 +24,7 @@
 
 #include <mp-units/bits/hacks.h>
 #include <mp-units/compat_macros.h>
+#include <mp-units/ext/contracts.h>
 #include <array>
 #include <compare>
 #include <concepts>
diff --git a/src/core/include/mp-units/bits/fmt.h b/src/core/include/mp-units/bits/fmt.h
index 8e84ac0b..bc3197e0 100644
--- a/src/core/include/mp-units/bits/fmt.h
+++ b/src/core/include/mp-units/bits/fmt.h
@@ -40,6 +40,7 @@
 #include <cstdint>
 #include <limits>
 #include <string_view>
+#include <mp-units/ext/contracts.h>
 #endif
 
 // most of the below code is based on/copied from fmtlib
diff --git a/src/core/include/mp-units/bits/ratio.h b/src/core/include/mp-units/bits/ratio.h
index bcf778dd..85e49afc 100644
--- a/src/core/include/mp-units/bits/ratio.h
+++ b/src/core/include/mp-units/bits/ratio.h
@@ -27,6 +27,7 @@
 #include <mp-units/compat_macros.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <mp-units/ext/contracts.h>
 #include <compare>  // IWYU pragma: export
 #include <cstdint>
 #include <numeric>
diff --git a/src/core/include/mp-units/compat_macros.h b/src/core/include/mp-units/compat_macros.h
index 026f04e9..1d9aff34 100644
--- a/src/core/include/mp-units/compat_macros.h
+++ b/src/core/include/mp-units/compat_macros.h
@@ -101,8 +101,6 @@ MP_UNITS_DIAGNOSTIC_POP
 
 #if MP_UNITS_API_CONTRACTS == 2 || __has_include(<gsl/gsl-lite.hpp>)
 
-#include <gsl/gsl-lite.hpp>
-
 #define MP_UNITS_EXPECTS(expr) gsl_Expects(expr)
 #define MP_UNITS_EXPECTS_DEBUG(expr) gsl_ExpectsDebug(expr)
 #define MP_UNITS_ASSERT(expr) gsl_Assert(expr)
@@ -110,9 +108,6 @@ MP_UNITS_DIAGNOSTIC_POP
 
 #elif MP_UNITS_API_CONTRACTS == 3 || __has_include(<gsl/gsl>)
 
-#include <gsl/gsl>
-#include <cassert>
-
 #define MP_UNITS_EXPECTS(expr) Expects(expr)
 #if defined NDEBUG
 #define MP_UNITS_EXPECTS_DEBUG(expr) static_cast<void>(0)
diff --git a/src/core/include/mp-units/ext/contracts.h b/src/core/include/mp-units/ext/contracts.h
new file mode 100644
index 00000000..b274b021
--- /dev/null
+++ b/src/core/include/mp-units/ext/contracts.h
@@ -0,0 +1,49 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2018 Mateusz Pusz
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// 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 MP_UNITS_IN_MODULE_INTERFACE
+
+#include <mp-units/bits/hacks.h>
+#include <mp-units/compat_macros.h>
+
+#if MP_UNITS_API_CONTRACTS == 2 || __has_include(<gsl/gsl-lite.hpp>)
+
+#if MP_UNITS_HOSTED
+#include <gsl/gsl-lite.hpp>
+#else
+#include <mp-units/bits/requires_hosted.h>
+#endif
+
+#elif MP_UNITS_API_CONTRACTS == 3 || __has_include(<gsl/gsl>)
+
+#if MP_UNITS_HOSTED
+#include <gsl/gsl>
+#include <cassert>
+#else
+#include <mp-units/bits/requires_hosted.h>
+#endif
+
+#endif
+
+#endif  // MP_UNITS_IN_MODULE_INTERFACE
diff --git a/src/core/include/mp-units/ext/fixed_string.h b/src/core/include/mp-units/ext/fixed_string.h
index 1cfe2369..2bfdb377 100644
--- a/src/core/include/mp-units/ext/fixed_string.h
+++ b/src/core/include/mp-units/ext/fixed_string.h
@@ -32,6 +32,7 @@
 #include <mp-units/ext/type_traits.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <mp-units/ext/contracts.h>
 #include <compare>  // IWYU pragma: export
 #include <cstddef>
 #include <cstdlib>
diff --git a/src/core/include/mp-units/framework/dimension.h b/src/core/include/mp-units/framework/dimension.h
index 4aa746dd..63f409de 100644
--- a/src/core/include/mp-units/framework/dimension.h
+++ b/src/core/include/mp-units/framework/dimension.h
@@ -34,6 +34,7 @@
 #include <mp-units/framework/symbol_text.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <mp-units/ext/contracts.h>
 #include <array>
 #include <cstdint>
 #include <iterator>
diff --git a/src/core/include/mp-units/framework/quantity.h b/src/core/include/mp-units/framework/quantity.h
index f9625a9d..a87fa251 100644
--- a/src/core/include/mp-units/framework/quantity.h
+++ b/src/core/include/mp-units/framework/quantity.h
@@ -37,6 +37,7 @@
 #include <mp-units/framework/unit_concepts.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <mp-units/ext/contracts.h>
 #include <compare>  // IWYU pragma: export
 #include <utility>
 #endif
diff --git a/src/core/include/mp-units/framework/symbol_text.h b/src/core/include/mp-units/framework/symbol_text.h
index e89aab96..a266cb24 100644
--- a/src/core/include/mp-units/framework/symbol_text.h
+++ b/src/core/include/mp-units/framework/symbol_text.h
@@ -31,6 +31,7 @@
 #include <mp-units/ext/fixed_string.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <mp-units/ext/contracts.h>
 #include <compare>  // IWYU pragma: export
 #include <cstddef>
 #include <cstdint>
diff --git a/src/core/include/mp-units/framework/unit.h b/src/core/include/mp-units/framework/unit.h
index c362afa1..e7786554 100644
--- a/src/core/include/mp-units/framework/unit.h
+++ b/src/core/include/mp-units/framework/unit.h
@@ -41,6 +41,7 @@
 #include <mp-units/framework/unit_concepts.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <mp-units/ext/contracts.h>
 #include <array>
 #include <cstdint>
 #include <iterator>