diff --git a/builder/build-wheels.sh b/builder/build-wheels.sh
index ffef437..e5c1b6f 100755
--- a/builder/build-wheels.sh
+++ b/builder/build-wheels.sh
@@ -8,7 +8,7 @@ yum install -y cmake3 gsl-devel zlib-devel
 ln -fs /usr/bin/cmake3 /usr/bin/cmake
 
 
-ALL_PYTHON="cp37-cp37m cp38-cp38" 
+ALL_PYTHON="cp36-cp36m cp37-cp37m cp38-cp38" 
 
 # Compile wheels
 for pkg in $ALL_PYTHON; do
diff --git a/builder/start.sh b/builder/start.sh
index 31f95f0..9fbc185 100755
--- a/builder/start.sh
+++ b/builder/start.sh
@@ -9,4 +9,4 @@ if ! [ -e ${d}/setup.py ] ; then
   exit 1
 fi
 
-podman run -ti  --rm -e PLAT=manylinux2014_x86_64 -v ${d}:/io:Z quay.io/pypa/manylinux2014_x86_64 /io/builder/build-wheels.sh
+podman run -ti  --rm -e PLAT=manylinux2010_x86_64 -v ${d}:/io:Z quay.io/pypa/manylinux2010_x86_64 /io/builder/build-wheels.sh
diff --git a/python/_cosmotool.pyx b/python/_cosmotool.pyx
index 61ba1a0..ed9195e 100644
--- a/python/_cosmotool.pyx
+++ b/python/_cosmotool.pyx
@@ -513,7 +513,8 @@ def writeGadget(str filename, object simulation):
   simdata.TotalNumPart = NumPart
   simdata.NumPart = NumPart
 
-  cxx_writeGadget(filename, &simdata)
+  filename_b = bytes(filename, 'utf-8')
+  cxx_writeGadget(filename_b, &simdata)
 
 def loadRamses(str basepath, int snapshot_id, int cpu_id, bool doublePrecision = False, bool loadPosition = True, bool loadVelocity = False, bool loadId = False, bool loadMass = False):
   """ loadRamses(basepath, snapshot_id, cpu_id, doublePrecision = False, loadPosition = True, loadVelocity = False)
diff --git a/python/cosmotool/simu.py b/python/cosmotool/simu.py
index 2389926..157e107 100644
--- a/python/cosmotool/simu.py
+++ b/python/cosmotool/simu.py
@@ -98,12 +98,12 @@ def simpleWriteGadget(filename, positions, boxsize=1.0, Hubble=100, Omega_M=0.30
   
   s.positions = positions
   
-  if velocities:
+  if velocities is not None:
     s.velocities = velocities
   else:
     s.velocities = [np.zeros(positions[0].size,dtype=np.float32)]*3
     
-  if identifiers:
+  if identifiers is not None:
     s.identifiers = identifiers
   else:
     s.identifiers = np.arange(positions[0].size, dtype=np.int64)