diff --git a/src/Makefile.am b/src/Makefile.am
index 6b663b9d4e50a3580238311ca45b13402f3067f3..095b11272dae027363628977c6b3098c3ab2a409 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -55,7 +55,7 @@ AM_SOURCES = space.c runner.c queue.c task.c cell.c engine.c \
     runner_doiact_fft.c threadpool.c cooling.c
 
 # Include files for distribution, not installation.
-nobase_noinst_HEADERS = approx_math.h atomic.h cycle.h error.h inline.h kernel_hydro.h kernel_gravity.h \
+nobase_noinst_HEADERS = align.h approx_math.h atomic.h cycle.h error.h inline.h kernel_hydro.h kernel_gravity.h \
 		 kernel_long_gravity.h vector.h runner_doiact.h runner_doiact_grav.h runner_doiact_fft.h \
                  units.h intrinsics.h minmax.h kick.h timestep.h drift.h adiabatic_index.h io_properties.h \
 		 dimension.h equation_of_state.h \
diff --git a/src/align.h b/src/align.h
new file mode 100644
index 0000000000000000000000000000000000000000..84e2909c0866c18f0f8378df9d0efc8d0f6545b5
--- /dev/null
+++ b/src/align.h
@@ -0,0 +1,27 @@
+/*******************************************************************************
+ * This file is part of SWIFT.
+ * Copyright (c) 2016 Matthieu Schaller (matthieu.schaller@durham.ac.uk).
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ ******************************************************************************/
+#ifndef SWIFT_ALIGN_H
+#define SWIFT_ALIGN_H
+
+/**
+ * @brief Defines alignment of structures
+ */
+#define SWIFT_STRUCT_ALIGN __attribute__((aligned(32)))
+
+#endif /* SWIFT_ALIGN_H */
diff --git a/src/cell.h b/src/cell.h
index 8e0494fa9db89b451a776140c18b57b54547120f..b78cc0a8f842770f60777e3986616a175d2f33ca 100644
--- a/src/cell.h
+++ b/src/cell.h
@@ -30,6 +30,7 @@
 #include <stddef.h>
 
 /* Local includes. */
+#include "align.h"
 #include "lock.h"
 #include "multipole.h"
 #include "part.h"
@@ -44,7 +45,7 @@ struct space;
  * The maximum was lowered by a further factor of 2 to be on the safe side.*/
 #define cell_max_tag (1 << 29)
 
-#define cell_align 32
+#define cell_align 128
 
 /* Global variables. */
 extern int cell_next_tag;
@@ -74,7 +75,8 @@ struct pcell {
 
   /* Relative indices of the cell's progeny. */
   int progeny[8];
-};
+
+} SWIFT_STRUCT_ALIGN;
 
 /* Structure to store the data of a single cell. */
 struct cell {
@@ -208,7 +210,7 @@ struct cell {
 
 #endif
 
-} __attribute__((aligned(cell_align)));
+} SWIFT_STRUCT_ALIGN;
 
 /* Convert cell location to ID. */
 #define cell_getid(cdim, i, j, k) \
diff --git a/src/gravity/Default/gravity_part.h b/src/gravity/Default/gravity_part.h
index 1850ff0a1644d3593f78f150646eae8b2f074e1e..f06e65e5b30ebcd609c0c6204de33da17b770add 100644
--- a/src/gravity/Default/gravity_part.h
+++ b/src/gravity/Default/gravity_part.h
@@ -53,6 +53,6 @@ struct gpart {
      which this gpart is linked. */
   long long id_or_neg_offset;
 
-} __attribute__((aligned(gpart_align)));
+} SWIFT_STRUCT_ALIGN;
 
 #endif /* SWIFT_DEFAULT_GRAVITY_PART_H */
diff --git a/src/hydro/Default/hydro_part.h b/src/hydro/Default/hydro_part.h
index 1b9dd01b845c5e0e7c29381c5136ee8dded54479..c7464bcf338b1c5b81ffa91d92264c2bd35e9313 100644
--- a/src/hydro/Default/hydro_part.h
+++ b/src/hydro/Default/hydro_part.h
@@ -38,7 +38,7 @@ struct xpart {
   /* Old density. */
   float omega;
 
-} __attribute__((aligned(xpart_align)));
+} SWIFT_STRUCT_ALIGN;
 
 /* Data of a single particle. */
 struct part {
@@ -125,6 +125,6 @@ struct part {
   /* Pointer to corresponding gravity part. */
   struct gpart* gpart;
 
-} __attribute__((aligned(part_align)));
+} SWIFT_STRUCT_ALIGN;
 
 #endif /* SWIFT_DEFAULT_HYDRO_PART_H */
diff --git a/src/hydro/Gadget2/hydro_part.h b/src/hydro/Gadget2/hydro_part.h
index 8ce279326e6aac7daace5006cffeca7735470395..0cdc1a8ab2b8d865f360dfba40486f3fb3056286 100644
--- a/src/hydro/Gadget2/hydro_part.h
+++ b/src/hydro/Gadget2/hydro_part.h
@@ -33,7 +33,7 @@ struct xpart {
   /* Additional data used to record cooling information */
   struct cooling_xpart_data cooling_data;
 
-} __attribute__((aligned(xpart_align)));
+} SWIFT_STRUCT_ALIGN;
 
 /* Data of a single particle. */
 struct part {
diff --git a/src/hydro/Gizmo/hydro_io.h b/src/hydro/Gizmo/hydro_io.h
index e5f221ae4345dc519a50d332131ecf296f318338..5de2260bf3046e0d09bf94aa56c4fb772045dac7 100644
--- a/src/hydro/Gizmo/hydro_io.h
+++ b/src/hydro/Gizmo/hydro_io.h
@@ -124,8 +124,8 @@ void hydro_write_particles(struct part* parts, struct io_props* list,
                                  UNIT_CONV_ACCELERATION, parts, a_hydro);
   list[7] = io_make_output_field("Density", FLOAT, 1, UNIT_CONV_DENSITY, parts,
                                  primitives.rho);
-  list[8] = io_make_output_field("Volume", FLOAT, 1, UNIT_CONV_VOLUME, parts,
-                                 geometry.volume);
+  list[8] = io_make_output_field("Volume", FLOAT, 1, UNIT_CONV_INV_VOLUME,
+                                 parts, geometry.volume);
   list[9] = io_make_output_field("GradDensity", FLOAT, 3, UNIT_CONV_DENSITY,
                                  parts, primitives.gradients.rho);
   list[10] = io_make_output_field_convert_part(
diff --git a/src/hydro/Gizmo/hydro_part.h b/src/hydro/Gizmo/hydro_part.h
index 781f078aa13c8ab4b02cb9509afe11fd47ed9774..16159bc8b958feaebf5fb9d17fb73832057d4573 100644
--- a/src/hydro/Gizmo/hydro_part.h
+++ b/src/hydro/Gizmo/hydro_part.h
@@ -33,7 +33,7 @@ struct xpart {
   /* Additional data used to record cooling information */
   struct cooling_xpart_data cooling_data;
 
-} __attribute__((aligned(xpart_align)));
+} SWIFT_STRUCT_ALIGN;
 
 /* Data of a single particle. */
 struct part {
@@ -204,5 +204,3 @@ struct part {
   struct gpart *gpart;
 
 } __attribute__((aligned(part_align)));
-
-#endif /* SWIFT_GIZMO_HYDRO_PART_H */
diff --git a/src/hydro/Minimal/hydro_part.h b/src/hydro/Minimal/hydro_part.h
index 8b1b2f74203b32809ed3f4d2305ce660ab3dd0b5..c83797b42b73f8cd8dd5bc993053769ba0cd354e 100644
--- a/src/hydro/Minimal/hydro_part.h
+++ b/src/hydro/Minimal/hydro_part.h
@@ -52,7 +52,7 @@ struct xpart {
   struct cooling_xpart_data
       cooling_data; /*!< Additional data used to record cooling information */
 
-} __attribute__((aligned(xpart_align)));
+} SWIFT_STRUCT_ALIGN;
 
 /**
  * @brief Particle fields for the SPH particles
diff --git a/src/part.h b/src/part.h
index ea895e6e0295d6a8b63309c7bd6855daa2cf7d64..af39d10fafc11d4435ddbcc087fbf08178b18959 100644
--- a/src/part.h
+++ b/src/part.h
@@ -31,12 +31,13 @@
 #endif
 
 /* Local headers. */
+#include "align.h"
 #include "const.h"
 
 /* Some constants. */
-#define part_align 64
-#define xpart_align 32
-#define gpart_align 32
+#define part_align 128
+#define xpart_align 128
+#define gpart_align 128
 
 /* Import the right hydro particle definition */
 #if defined(MINIMAL_SPH)
diff --git a/src/task.h b/src/task.h
index f070451fe4e79e0c16dc3dcca1ce145c08841c47..4928dc00bcd7958efdd6987b5aec90ab4b3e92fa 100644
--- a/src/task.h
+++ b/src/task.h
@@ -26,6 +26,7 @@
 #include "../config.h"
 
 /* Includes. */
+#include "align.h"
 #include "cell.h"
 #include "cycle.h"
 
@@ -149,7 +150,7 @@ struct task {
   /*! Is this task implicit (i.e. does not do anything) ? */
   char implicit;
 
-} __attribute__((aligned(32)));
+} SWIFT_STRUCT_ALIGN;
 
 /* Function prototypes. */
 void task_unlock(struct task *t);
diff --git a/src/units.c b/src/units.c
index f598b5ddf0b1a4b165648d5378915cd6f10f0bba..2241d441ec9af9b6d5083191e8f61010ebaccb20 100644
--- a/src/units.c
+++ b/src/units.c
@@ -319,6 +319,9 @@ void units_get_base_unit_exponants_array(float baseUnitsExp[5],
       break;
 
     case UNIT_CONV_VOLUME:
+      baseUnitsExp[UNIT_LENGTH] = 3.f;
+
+    case UNIT_CONV_INV_VOLUME:
       baseUnitsExp[UNIT_LENGTH] = -3.f;
   }
 }
diff --git a/src/units.h b/src/units.h
index 26fa15a66528dd39ea232cdf94da2ff0230300cd..78fdf1c23c3c276607d5353ee3437d8eb1e96537 100644
--- a/src/units.h
+++ b/src/units.h
@@ -90,7 +90,8 @@ enum UnitConversionFactor {
   UNIT_CONV_MAGNETIC_FIELD,
   UNIT_CONV_MAGNETIC_INDUCTANCE,
   UNIT_CONV_TEMPERATURE,
-  UNIT_CONV_VOLUME
+  UNIT_CONV_VOLUME,
+  UNIT_CONV_INV_VOLUME
 };
 
 void units_init_cgs(struct UnitSystem*);
diff --git a/tests/testSPHStep.c b/tests/testSPHStep.c
index fa49ed9d00c37393abd2f7e17ae628d79b4125f6..ff2ec841b27bd5ca6190517bc39f4da0c28fbc0c 100644
--- a/tests/testSPHStep.c
+++ b/tests/testSPHStep.c
@@ -102,10 +102,6 @@ int main() {
 
   int i, j, k, offset[3];
   struct part *p;
-  struct hydro_props hp;
-  hp.target_neighbours = 48.;
-  hp.delta_neighbours = 1.;
-  hp.max_smoothing_iterations = 30;
 
   int N = 10;
   float dim = 1.;
@@ -146,11 +142,24 @@ int main() {
   /* Create the infrastructure */
   struct space space;
   space.periodic = 0;
-  space.h_max = 1.;
+  space.cell_min = 1.;
+
+  struct phys_const prog_const;
+  prog_const.const_newton_G = 1.f;
+
+  struct hydro_props hp;
+  hp.target_neighbours = 48.f;
+  hp.delta_neighbours = 2.;
+  hp.max_smoothing_iterations = 1;
+  hp.CFL_condition = 0.1;
 
   struct engine e;
-  e.s = &space;
+  bzero(&e, sizeof(struct engine));
   e.hydro_properties = &hp;
+  e.physical_constants = &prog_const;
+  e.s = &space;
+  e.time = 0.1f;
+  e.ti_current = 1;
 
   struct runner r;
   r.e = &e;