diff --git a/src/io/io.f90 b/src/io/io.f90
index b951130d1..51d10561d 100644
--- a/src/io/io.f90
+++ b/src/io/io.f90
@@ -603,7 +603,7 @@ module subroutine io_param_reader(self, unit, iotype, v_list, iostat, iomsg)
                   if (param_value == "YES" .or. param_value == 'T') param%ltides = .true. 
                case ("FLATTEN_INTERACTIONS")
                   call io_toupper(param_value)
-                  if (param_value == "YES" .or. param_value == 'T') param%lflatten_interactions = .false.
+                  if (param_value == "NO" .or. param_value == 'F') param%lflatten_interactions = .false.
                case ("FIRSTKICK")
                   call io_toupper(param_value)
                   if (param_value == "NO" .or. param_value == 'F') param%lfirstkick = .false. 
diff --git a/src/modules/swiftest_classes.f90 b/src/modules/swiftest_classes.f90
index 0842ab154..a1f60c0dd 100644
--- a/src/modules/swiftest_classes.f90
+++ b/src/modules/swiftest_classes.f90
@@ -133,7 +133,7 @@ module swiftest_classes
       logical :: loblatecb      = .false. !! Calculate acceleration from oblate central body (automatically turns true if nonzero J2 is input)
       logical :: lrotation      = .false. !! Include rotation states of big bodies
       logical :: ltides         = .false. !! Include tidal dissipation 
-      logical :: lflatten_interactions = .false. !! Use the flattened upper triangular matrix for pl-pl interactions (turning this on improves the speed but uses more memory)
+      logical :: lflatten_interactions = .true. !! Use the flattened upper triangular matrix for pl-pl interactions (turning this on improves the speed but uses more memory)
 
       ! Initial values to pass to the energy report subroutine (usually only used in the case of a restart, otherwise these will be updated with initial conditions values)
       real(DP)                  :: Eorbit_orig = 0.0_DP   !! Initial orbital energy