diff --git a/include/boost/math/special_functions/detail/bessel_ik.hpp b/include/boost/math/special_functions/detail/bessel_ik.hpp
index 0c653b4753..2ffb0f060c 100644
--- a/include/boost/math/special_functions/detail/bessel_ik.hpp
+++ b/include/boost/math/special_functions/detail/bessel_ik.hpp
@@ -326,6 +326,11 @@ 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
@@ -337,11 +342,6 @@ 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
@@ -414,6 +414,7 @@ int bessel_ik(T v, T x, T* result_I, T* result_K, int kind, const Policy& pol)
     }
     if (reflect)
     {
+        BOOST_MATH_ASSERT(fabs(v - n - u) < tools::forth_root_epsilon<T>());
         T z = (u + n % 2);
         T fact = (2 / pi<T>()) * (boost::math::sin_pi(z, pol) * Kv);
         if(fact == 0)
diff --git a/test/test_bessel_j.hpp b/test/test_bessel_j.hpp
index 82106213ea..c54ad4fa8b 100644
--- a/test/test_bessel_j.hpp
+++ b/test/test_bessel_j.hpp
@@ -288,6 +288,7 @@ void test_bessel(T, const char* name)
        BOOST_CHECK_EQUAL(boost::math::cyl_bessel_j(T(0), std::numeric_limits<T>::infinity()), T(0));
        BOOST_CHECK_EQUAL(boost::math::cyl_bessel_j(T(2), std::numeric_limits<T>::infinity()), T(0));
        BOOST_CHECK_EQUAL(boost::math::cyl_bessel_j(T(1.25), std::numeric_limits<T>::infinity()), T(0));
+       BOOST_CHECK_EQUAL(boost::math::cyl_bessel_j(T(-1.25), std::numeric_limits<T>::infinity()), T(0));
        BOOST_CHECK_EQUAL(boost::math::sph_bessel(0, std::numeric_limits<T>::infinity()), T(0));
        BOOST_CHECK_EQUAL(boost::math::sph_bessel(1, std::numeric_limits<T>::infinity()), T(0));
        BOOST_CHECK_EQUAL(boost::math::sph_bessel(2, std::numeric_limits<T>::infinity()), T(0));