diff --git a/modules/installer/cd-dvd/iso-image.nix b/modules/installer/cd-dvd/iso-image.nix
index 33000a3fbf1..27e731d61e8 100644
--- a/modules/installer/cd-dvd/iso-image.nix
+++ b/modules/installer/cd-dvd/iso-image.nix
@@ -208,14 +208,14 @@ in
       mkdir /unionfs-chroot/rw-root
       mount -t tmpfs -o "mode=755" none /unionfs-chroot/rw-root
       mkdir /mnt-root-union
-      unionfs -o allow_other,cow,chroot=/unionfs-chroot /rw-root=RW:/ro-root=RO /mnt-root-union
+      unionfs -o allow_other,cow,chroot=/unionfs-chroot,max_files=32768 /rw-root=RW:/ro-root=RO /mnt-root-union
       oldTargetRoot=$targetRoot
       targetRoot=/mnt-root-union
 
       mkdir /unionfs-chroot/rw-store
       mount -t tmpfs -o "mode=755" none /unionfs-chroot/rw-store
       mkdir -p $oldTargetRoot/nix/store
-      unionfs -o allow_other,cow,nonempty,chroot=/unionfs-chroot /rw-store=RW:/ro-root/nix/store=RO /mnt-root-union/nix/store
+      unionfs -o allow_other,cow,nonempty,chroot=/unionfs-chroot,max_files=32768 /rw-store=RW:/ro-root/nix/store=RO /mnt-root-union/nix/store
     '';
 
   # Closures to be copied to the Nix store on the CD, namely the init
diff --git a/modules/virtualisation/amazon-image.nix b/modules/virtualisation/amazon-image.nix
index 38885d12b35..aa0a97d3aa0 100644
--- a/modules/virtualisation/amazon-image.nix
+++ b/modules/virtualisation/amazon-image.nix
@@ -132,7 +132,7 @@ with pkgs.lib;
               mkdir -p /unionfs-chroot/rw-nix
               mount --rbind $targetRoot/$diskForUnionfs/root/nix /unionfs-chroot/rw-nix
 
-              unionfs -o allow_other,cow,nonempty,chroot=/unionfs-chroot /rw-nix=RW:/ro-nix=RO $targetRoot/nix
+              unionfs -o allow_other,cow,nonempty,chroot=/unionfs-chroot,max_files=32768 /rw-nix=RW:/ro-nix=RO $targetRoot/nix
           fi
       fi
     '';
diff --git a/modules/virtualisation/nova-image.nix b/modules/virtualisation/nova-image.nix
index 0ce5d218cdb..cc012ffc8a3 100644
--- a/modules/virtualisation/nova-image.nix
+++ b/modules/virtualisation/nova-image.nix
@@ -98,7 +98,7 @@ with pkgs.lib;
       mkdir -p /unionfs-chroot/rw-nix
       mkdir -m 755 -p $targetRoot/ephemeral0/nix
       mount --rbind $targetRoot/ephemeral0/nix /unionfs-chroot/rw-nix
-      unionfs -o allow_other,cow,nonempty,chroot=/unionfs-chroot /rw-nix=RW:/ro-nix=RO $targetRoot/nix
+      unionfs -o allow_other,cow,nonempty,chroot=/unionfs-chroot,max_files=32768 /rw-nix=RW:/ro-nix=RO $targetRoot/nix
     '';
 
     boot.initrd.supportedFilesystems = [ "unionfs-fuse" ];
diff --git a/modules/virtualisation/qemu-vm.nix b/modules/virtualisation/qemu-vm.nix
index b35b311819a..9d9581b96c6 100644
--- a/modules/virtualisation/qemu-vm.nix
+++ b/modules/virtualisation/qemu-vm.nix
@@ -281,7 +281,7 @@ in
       # Mark this as a NixOS machinex.
       mkdir -p $targetRoot/etc
       echo -n > $targetRoot/etc/NIXOS
-    
+
       # Fix the permissions on /tmp.
       chmod 1777 $targetRoot/tmp
 
@@ -293,7 +293,7 @@ in
 
         mkdir /unionfs-chroot/rw-store
         mount -t tmpfs -o "mode=755" none /unionfs-chroot/rw-store
-        unionfs -o allow_other,cow,nonempty,chroot=/unionfs-chroot /rw-store=RW:/ro-store=RO $targetRoot/nix/store
+        unionfs -o allow_other,cow,nonempty,chroot=/unionfs-chroot,max_files=32768 /rw-store=RW:/ro-store=RO $targetRoot/nix/store
       ''}
     '';