diff --git a/TurTLE/test/test_particle_set_init.py b/TurTLE/test/test_particle_set_init.py
index d6f352c284f4d6c211d1f3eddfc1c7b0c88712f5..5af878645515bdbc4bf84191d7384f67871cea86 100644
--- a/TurTLE/test/test_particle_set_init.py
+++ b/TurTLE/test/test_particle_set_init.py
@@ -44,7 +44,7 @@ class aTEST(TEST):
         self.includes = '\n'.join(
                 ['#include ' + hh
                  for hh in self.include_list])
-        self.definitions += open(
+        self.definitions = open(
             os.path.join(
                 cpp_location, self.dns_type + '.hpp'), 'r').read()
         self.definitions += open(