diff --git a/src/OPENMP/angle_cosine_periodic_omp.cpp b/src/OPENMP/angle_cosine_periodic_omp.cpp
index 43b3a54a47..48532c8f6c 100644
--- a/src/OPENMP/angle_cosine_periodic_omp.cpp
+++ b/src/OPENMP/angle_cosine_periodic_omp.cpp
@@ -140,7 +140,7 @@ void AngleCosinePeriodicOMP::eval(int nfrom, int nto, ThrData * const thr)
     tn = 1.0;
     tn_1 = 1.0;
     tn_2 = 0.0;
-    un = 1.0;
+    un = (m==1) ? 2.0 : 1.0;
     un_1 = 2.0;
     un_2 = 0.0;