diff --git a/CHANGELOG.md b/CHANGELOG.md
index 14b021a..d267ff7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 * Added support for free-threaded (GIL-disabled) CPython builds: the Cython extension is compiled with `freethreading_compatible=True` and `_mklinit` declares `Py_MOD_GIL_NOT_USED`, so importing `mkl` no longer re-enables the GIL [gh-213](https://github.com/IntelPython/mkl-service/pull/213)
+* Added support for new build option `ilp64` to initialize MKL with the ILP64 interface, which also resolves some build warnings [gh-184](https://github.com/IntelPython/mkl-service/pull/184)
 
 ### Changed
 * Raised the minimum build-time `Cython` requirement to `3.1.0`, the first release providing the `freethreading_compatible` directive [gh-213](https://github.com/IntelPython/mkl-service/pull/213)
diff --git a/README.md b/README.md
index 52620af..3eb6e97 100644
--- a/README.md
+++ b/README.md
@@ -54,3 +54,36 @@ then build against the existing installation with:
 ```sh
 python -m pip install --no-build-isolation --no-deps .
 ```
+
+### Build options
+
+| Option  | Type    | Default | Description                           |
+| ------- | ------- | ------- | ------------------------------------- |
+| `ilp64` | boolean | `false` | Build with the oneMKL ILP64 interface |
+
+Options are passed using `-Csetup-args`:
+```sh
+python -m pip install . -Csetup-args=-Dilp64=true
+```
+
+By default `mkl-service` is built against the LP64 interface, in which oneMKL's
+integer type `MKL_INT` is 32-bit. Enabling `ilp64` makes `MKL_INT` 64-bit
+and requests the ILP64 interface layer from `libmkl_rt` on import.
+Use it when the oneMKL libraries you link against provide the ILP64 interface.
+
+The Python API is identical in both configurations — no function signature or
+return value changes.
+
+> **Warning:** the oneMKL interface layer is process-global and can only be
+> selected before the first oneMKL call. `mkl-service` requests it on import,
+> so an ILP64 build is order-dependent and unsafe to mix with LP64
+> consumers:
+>
+> * If imported before another oneMKL consumer initializes oneMKL, that
+>   consumer's LP64 calls get reinterpreted as ILP64. LAPACK routines in
+>   particular may crash.
+> * If the other consumer initializes oneMKL first, the ILP64 request is ignored
+>   and the process stays LP64.
+>
+> Only enable `ilp64` when every consumer uses the ILP64 interface or
+> `mkl-service` is the sole oneMKL consumer in the process.
diff --git a/meson.build b/meson.build
index 1b9ce89..0972a6b 100644
--- a/meson.build
+++ b/meson.build
@@ -15,6 +15,12 @@ project(
 py = import('python').find_installation(pure: false)
 
 c_args = ['-DNDEBUG']
+cmake_mkl_interface = 'lp64'
+
+if get_option('ilp64')
+    c_args += '-DMKL_ILP64'
+    cmake_mkl_interface = 'ilp64'
+endif
 
 thread_dep = dependency('threads')
 
@@ -24,6 +30,7 @@ mkl_dep = dependency('MKL', method: 'cmake',
     cmake_args: [
         '-DMKL_ARCH=intel64',
         '-DMKL_LINK=sdl',
+        '-DMKL_INTERFACE=' + cmake_mkl_interface,
     ],
     required: true
 )
diff --git a/meson.options b/meson.options
new file mode 100644
index 0000000..46117a3
--- /dev/null
+++ b/meson.options
@@ -0,0 +1,2 @@
+option('ilp64', type: 'boolean', value: false,
+    description: 'Build with MKL ILP64 interface')
diff --git a/mkl/_mkl_service.pxd b/mkl/_mkl_service.pxd
index 4cba157..ed5a106 100644
--- a/mkl/_mkl_service.pxd
+++ b/mkl/_mkl_service.pxd
@@ -24,12 +24,13 @@
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 
-ctypedef long long MKL_INT64
-ctypedef unsigned long long MKL_UINT64
-ctypedef int MKL_INT
-
-
 cdef extern from "mkl.h":
+    # defer definition of integer types to mkl.h
+    # Cython will narrow the types based on what mkl.h defines
+    ctypedef long long MKL_INT64
+    ctypedef unsigned long long MKL_UINT64
+    ctypedef long long MKL_INT
+
     # MKL Function Domains Constants
     int MKL_DOMAIN_BLAS
     int MKL_DOMAIN_FFT
diff --git a/mkl/_mklinitmodule.c b/mkl/_mklinitmodule.c
index 5a65b73..996ea59 100644
--- a/mkl/_mklinitmodule.c
+++ b/mkl/_mklinitmodule.c
@@ -25,8 +25,11 @@ static struct PyMethodDef methods[] = {{NULL, NULL, 0, NULL}};
 #define MKL_SERVICE_INLINE inline
 #endif
 
+#ifdef MKL_ILP64
 static MKL_SERVICE_INLINE void _set_mkl_ilp64(void);
+#else
 static MKL_SERVICE_INLINE void _set_mkl_lp64(void);
+#endif
 static MKL_SERVICE_INLINE void _set_mkl_interface(void);
 
 static const char *mtlayer;
@@ -151,6 +154,7 @@ static void _preload_threading_layer(void)
     return;
 }
 
+#ifdef MKL_ILP64
 static MKL_SERVICE_INLINE void _set_mkl_ilp64(void)
 {
 #ifdef USING_MKL_RT
@@ -158,7 +162,7 @@ static MKL_SERVICE_INLINE void _set_mkl_ilp64(void)
 #endif
     return;
 }
-
+#else
 static MKL_SERVICE_INLINE void _set_mkl_lp64(void)
 {
 #ifdef USING_MKL_RT
@@ -166,10 +170,15 @@ static MKL_SERVICE_INLINE void _set_mkl_lp64(void)
 #endif
     return;
 }
+#endif
 
 static MKL_SERVICE_INLINE void _set_mkl_interface(void)
 {
+#ifdef MKL_ILP64
+    _set_mkl_ilp64();
+#else
     _set_mkl_lp64();
+#endif
     _preload_threading_layer();
 }