diff --git a/include/fem.hpp b/include/fem.hpp
index 3cf1cbcdc16de910a2582d2c657ea358065fc294..6460545760bdb47ee01a1416c8e63d69480ad265 100644
--- a/include/fem.hpp
+++ b/include/fem.hpp
@@ -81,8 +81,8 @@ auto triangledata<T>::intsing(T x0, T y0, T z0) const
 {
     // initialize
     std::size_t ip, ipp;
-    static matrix<T> xX0S(1,3), yX0S(1,3), zX0S(1,3);
-    static matrix<T> nrmX0S(1,3), ca(1,3), sa(1,3), xnu(1,3);
+    matrix<T> xX0S(1,3), yX0S(1,3), zX0S(1,3);
+    matrix<T> nrmX0S(1,3), ca(1,3), sa(1,3), xnu(1,3);
     T omega, h, ps, psp1, ps2, ah, ar, intaRm1;
     T Rm1, dnRm1;
     T tol = 1e-7;