diff --git a/include/boost/math/special_functions/detail/bessel_ik.hpp b/include/boost/math/special_functions/detail/bessel_ik.hpp
index a342ccf0c..badb70dee 100644
--- a/include/boost/math/special_functions/detail/bessel_ik.hpp
+++ b/include/boost/math/special_functions/detail/bessel_ik.hpp
@@ -327,6 +327,11 @@ int bessel_ik(T v, T x, T* result_I, T* result_K, int kind, const Policy& pol)
     T scale = 1;
     T scale_sign = 1;
 
+    n = iround(v, pol);
+    u = v - n;                              // -1/2 <= u < 1/2
+    BOOST_MATH_INSTRUMENT_VARIABLE(n);
+    BOOST_MATH_INSTRUMENT_VARIABLE(u);
+
     if (((kind & need_i) == 0) && (fabs(4 * v * v - 25) / (8 * x) < tools::forth_root_epsilon<T>()))
     {
        // A&S 9.7.2
@@ -338,11 +343,6 @@ int bessel_ik(T v, T x, T* result_I, T* result_K, int kind, const Policy& pol)
     }
     else
     {
-       n = iround(v, pol);
-       u = v - n;                              // -1/2 <= u < 1/2
-       BOOST_MATH_INSTRUMENT_VARIABLE(n);
-       BOOST_MATH_INSTRUMENT_VARIABLE(u);
-
        BOOST_MATH_ASSERT(x > 0); // Error handling for x <= 0 handled in cyl_bessel_i and cyl_bessel_k
 
        // x is positive until reflection