diff --git a/WENO.F90 b/WENO.F90
index a6da580111b2bf9cc9365eeb7f3732fb1ae0b3d5..e8618ef65764d2f64d310a023855a0651cfe8652 100644
--- a/WENO.F90
+++ b/WENO.F90
@@ -913,7 +913,7 @@ subroutine mult_mat_vec(m, n, alpha, a, b, c)
     do j=1,n
       accumulator = accumulator + alpha*a(i,j)*b(j)
     end do
-    c(i) = c(i) + accumulator
+    c(i) = accumulator
   end do
 end subroutine
 
diff --git a/test.py b/test.py
index 2446f40d8f33b00d92bbcfec0ad655d51a601f71..84ce34cd09065f089a920d1a8778f269720d3a1a 100644
--- a/test.py
+++ b/test.py
@@ -8,6 +8,7 @@ import sys
 
 import logging
 
+import pytest
 from pyopencl.tools import (  # noqa
         pytest_generate_tests_for_pyopencl
         as pytest_generate_tests)