diff --git a/nixos/modules/virtualisation/qemu-vm.nix b/nixos/modules/virtualisation/qemu-vm.nix
index b1f36cf32644..0cefd618075c 100644
--- a/nixos/modules/virtualisation/qemu-vm.nix
+++ b/nixos/modules/virtualisation/qemu-vm.nix
@@ -426,19 +426,19 @@ in
         ${if cfg.writableStore then "/nix/.ro-store" else "/nix/store"} =
           { device = "store";
             fsType = "9p";
-            options = "trans=virtio,version=9p2000.L,msize=1048576,cache=loose";
+            options = "trans=virtio,version=9p2000.L,cache=loose";
             neededForBoot = true;
           };
         "/tmp/xchg" =
           { device = "xchg";
             fsType = "9p";
-            options = "trans=virtio,version=9p2000.L,msize=1048576,cache=loose";
+            options = "trans=virtio,version=9p2000.L,cache=loose";
             neededForBoot = true;
           };
         "/tmp/shared" =
           { device = "shared";
             fsType = "9p";
-            options = "trans=virtio,version=9p2000.L,msize=1048576";
+            options = "trans=virtio,version=9p2000.L";
             neededForBoot = true;
           };
       } // optionalAttrs cfg.writableStore
diff --git a/pkgs/build-support/vm/default.nix b/pkgs/build-support/vm/default.nix
index 250f2b0fbce7..ebcbf8c87b5e 100644
--- a/pkgs/build-support/vm/default.nix
+++ b/pkgs/build-support/vm/default.nix
@@ -118,7 +118,7 @@ rec {
 
     echo "mounting Nix store..."
     mkdir -p /fs/nix/store
-    mount -t 9p store /fs/nix/store -o trans=virtio,version=9p2000.L,msize=262144,cache=loose
+    mount -t 9p store /fs/nix/store -o trans=virtio,version=9p2000.L,cache=loose
 
     mkdir -p /fs/tmp /fs/run /fs/var
     mount -t tmpfs -o "mode=1777" none /fs/tmp
@@ -127,7 +127,7 @@ rec {
 
     echo "mounting host's temporary directory..."
     mkdir -p /fs/tmp/xchg
-    mount -t 9p xchg /fs/tmp/xchg -o trans=virtio,version=9p2000.L,msize=262144,cache=loose
+    mount -t 9p xchg /fs/tmp/xchg -o trans=virtio,version=9p2000.L,cache=loose
 
     mkdir -p /fs/proc
     mount -t proc none /fs/proc
diff --git a/pkgs/build-support/vm/windows/controller/default.nix b/pkgs/build-support/vm/windows/controller/default.nix
index 0beaf401758a..1c8e6af83b86 100644
--- a/pkgs/build-support/vm/windows/controller/default.nix
+++ b/pkgs/build-support/vm/windows/controller/default.nix
@@ -48,11 +48,11 @@ let
     mount -t proc none /fs/proc
 
     mount -t 9p \
-      -o trans=virtio,version=9p2000.L,msize=262144,cache=loose \
+      -o trans=virtio,version=9p2000.L,cache=loose \
       store /fs/nix/store
 
     mount -t 9p \
-      -o trans=virtio,version=9p2000.L,msize=262144,cache=loose \
+      -o trans=virtio,version=9p2000.L,cache=loose \
       xchg /fs/xchg
 
     echo root:x:0:0::/root:/bin/false > /fs/etc/passwd