diff --git a/README.md b/README.md
index b79e44a..580111f 100644
--- a/README.md
+++ b/README.md
@@ -57,7 +57,7 @@ data types.
 ## Arg sort routines on arrays
 ```cpp
 std::vector<size_t> arg = x86simdsort::argsort(const T* arr, size_t size, bool hasnan, bool descending);
-std::vector<size_t> arg = x86simdsort::argselect(T* arr, size_t k, size_t size, bool hasnan);
+std::vector<size_t> arg = x86simdsort::argselect(const T* arr, size_t k, size_t size, bool hasnan);
 ```
 Supported datatypes: `T` $\in$ `[_Float16, uint16_t, int16_t, float, uint32_t, int32_t, double,
 uint64_t, int64_t]` Note that argsort and argselect are not accelerated with SIMD when using 16-bit
diff --git a/lib/x86simdsort-avx2.cpp b/lib/x86simdsort-avx2.cpp
index 1e0761e..36b43e8 100644
--- a/lib/x86simdsort-avx2.cpp
+++ b/lib/x86simdsort-avx2.cpp
@@ -29,7 +29,7 @@
     } \
     template <> \
     std::vector<size_t> argselect( \
-            type *arr, size_t k, size_t arrsize, bool hasnan) \
+            const type *arr, size_t k, size_t arrsize, bool hasnan) \
     { \
         return x86simdsortStatic::argselect(arr, k, arrsize, hasnan); \
     }
diff --git a/lib/x86simdsort-internal.h b/lib/x86simdsort-internal.h
index f8a14c0..055df2b 100644
--- a/lib/x86simdsort-internal.h
+++ b/lib/x86simdsort-internal.h
@@ -50,7 +50,7 @@
                                                 bool descending = false); \
     template <typename T> \
     XSS_HIDE_SYMBOL std::vector<size_t> \
-    argselect(T *arr, size_t k, size_t arrsize, bool hasnan = false); \
+    argselect(const T *arr, size_t k, size_t arrsize, bool hasnan = false); \
     }
 
 namespace xss {
diff --git a/lib/x86simdsort-scalar.h b/lib/x86simdsort-scalar.h
index 95fab42..9f08f9b 100644
--- a/lib/x86simdsort-scalar.h
+++ b/lib/x86simdsort-scalar.h
@@ -88,7 +88,8 @@ namespace scalar {
         return arg;
     }
     template <typename T>
-    std::vector<size_t> argselect(T *arr, size_t k, size_t arrsize, bool hasnan)
+    std::vector<size_t>
+    argselect(const T *arr, size_t k, size_t arrsize, bool hasnan)
     {
         UNUSED(hasnan);
         std::vector<size_t> arg(arrsize);
diff --git a/lib/x86simdsort-skx.cpp b/lib/x86simdsort-skx.cpp
index f4c4125..6260bab 100644
--- a/lib/x86simdsort-skx.cpp
+++ b/lib/x86simdsort-skx.cpp
@@ -29,7 +29,7 @@
     } \
     template <> \
     std::vector<size_t> argselect( \
-            type *arr, size_t k, size_t arrsize, bool hasnan) \
+            const type *arr, size_t k, size_t arrsize, bool hasnan) \
     { \
         return x86simdsortStatic::argselect(arr, k, arrsize, hasnan); \
     }
diff --git a/lib/x86simdsort.cpp b/lib/x86simdsort.cpp
index 7aecbea..35d6ce4 100644
--- a/lib/x86simdsort.cpp
+++ b/lib/x86simdsort.cpp
@@ -99,11 +99,11 @@ namespace x86simdsort {
 
 #define DECLARE_INTERNAL_argselect(TYPE) \
     static std::vector<size_t> (*internal_argselect##TYPE)( \
-            TYPE *, size_t, size_t, bool) \
+            const TYPE *, size_t, size_t, bool) \
             = NULL; \
     template <> \
     std::vector<size_t> argselect( \
-            TYPE *arr, size_t k, size_t arrsize, bool hasnan) \
+            const TYPE *arr, size_t k, size_t arrsize, bool hasnan) \
     { \
         return (*internal_argselect##TYPE)(arr, k, arrsize, hasnan); \
     }
diff --git a/lib/x86simdsort.h b/lib/x86simdsort.h
index c410918..34ed101 100644
--- a/lib/x86simdsort.h
+++ b/lib/x86simdsort.h
@@ -43,7 +43,7 @@ XSS_EXPORT_SYMBOL std::vector<size_t> argsort(const T *arr,
 // argselect
 template <typename T>
 XSS_EXPORT_SYMBOL std::vector<size_t>
-argselect(T *arr, size_t k, size_t arrsize, bool hasnan = false);
+argselect(const T *arr, size_t k, size_t arrsize, bool hasnan = false);
 
 // keyvalue sort
 template <typename T1, typename T2>
diff --git a/src/README.md b/src/README.md
index 2e52a45..ad5fc7b 100644
--- a/src/README.md
+++ b/src/README.md
@@ -75,7 +75,7 @@ Equivalent to `np.argselect` in
 [NumPy](https://numpy.org/doc/stable/reference/generated/numpy.argpartition.html).
 
 ```cpp
-void x86simdsortStatic::argselect<T>(T* arr, size_t *arg, size_t k, size_t arrsize, bool hasnan = false);
+void x86simdsortStatic::argselect<T>(const T* arr, size_t *arg, size_t k, size_t arrsize, bool hasnan = false);
 ```
 Supported datatypes: `uint32_t`, `int32_t`, `float`, `uint64_t`, `int64_t` and
 `double`.
diff --git a/src/x86simdsort-static-incl.h b/src/x86simdsort-static-incl.h
index 852da1f..2b0a11e 100644
--- a/src/x86simdsort-static-incl.h
+++ b/src/x86simdsort-static-incl.h
@@ -40,12 +40,12 @@ X86_SIMD_SORT_FINLINE void argsort(const T *arr,
 
 template <typename T>
 X86_SIMD_SORT_FINLINE std::vector<size_t>
-argselect(T *arr, size_t k, size_t size, bool hasnan = false);
+argselect(const T *arr, size_t k, size_t size, bool hasnan = false);
 
 /* argselect API required by NumPy: */
 template <typename T>
-void X86_SIMD_SORT_FINLINE
-argselect(T *arr, size_t *arg, size_t k, size_t size, bool hasnan = false);
+void X86_SIMD_SORT_FINLINE argselect(
+        const T *arr, size_t *arg, size_t k, size_t size, bool hasnan = false);
 
 template <typename T1, typename T2>
 X86_SIMD_SORT_FINLINE void keyvalue_qsort(T1 *key,
@@ -112,13 +112,13 @@ X86_SIMD_SORT_FINLINE void keyvalue_partial_sort(T1 *key,
     } \
     template <typename T> \
     X86_SIMD_SORT_FINLINE void x86simdsortStatic::argselect( \
-            T *arr, size_t *arg, size_t k, size_t size, bool hasnan) \
+            const T *arr, size_t *arg, size_t k, size_t size, bool hasnan) \
     { \
         ISA##_argselect(arr, arg, k, size, hasnan); \
     } \
     template <typename T> \
     X86_SIMD_SORT_FINLINE std::vector<size_t> x86simdsortStatic::argselect( \
-            T *arr, size_t k, size_t size, bool hasnan) \
+            const T *arr, size_t k, size_t size, bool hasnan) \
     { \
         std::vector<size_t> indices(size); \
         std::iota(indices.begin(), indices.end(), 0); \
diff --git a/src/xss-common-argsort.h b/src/xss-common-argsort.h
index 9af9e70..3e80083 100644
--- a/src/xss-common-argsort.h
+++ b/src/xss-common-argsort.h
@@ -741,7 +741,10 @@ X86_SIMD_SORT_INLINE void avx512_argselect(T *arr,
                                            arrsize_t arrsize,
                                            bool hasnan = false)
 {
-    xss_argselect<T, zmm_vector, ymm_vector>(arr, arg, k, arrsize, hasnan);
+    // Safe: argselect never mutates arr; const is dropped only for SIMD type instantiation
+    using base_t = std::remove_const_t<T>;
+    xss_argselect<base_t, zmm_vector, ymm_vector>(
+            const_cast<base_t *>(arr), arg, k, arrsize, hasnan);
 }
 
 template <typename T>
@@ -751,8 +754,10 @@ X86_SIMD_SORT_INLINE void avx2_argselect(T *arr,
                                          arrsize_t arrsize,
                                          bool hasnan = false)
 {
-    xss_argselect<T, avx2_vector, avx2_half_vector>(
-            arr, arg, k, arrsize, hasnan);
+    // Safe: argselect never mutates arr; const is dropped only for SIMD type instantiation
+    using base_t = std::remove_const_t<T>;
+    xss_argselect<base_t, avx2_vector, avx2_half_vector>(
+            const_cast<base_t *>(arr), arg, k, arrsize, hasnan);
 }
 
 #endif // XSS_COMMON_ARGSORT