diff --git a/pkgs/build-support/vm/default.nix b/pkgs/build-support/vm/default.nix
index d2aeb784e7fd..a6633d11286f 100644
--- a/pkgs/build-support/vm/default.nix
+++ b/pkgs/build-support/vm/default.nix
@@ -390,7 +390,7 @@ rec {
       diskImage=$(pwd)/disk-image.qcow2
       origImage=${attrs.diskImage}
       if test -d "$origImage"; then origImage="$origImage/disk-image.qcow2"; fi
-      ${qemu}/bin/qemu-img create -b "$origImage" -f qcow2 $diskImage
+      ${qemu}/bin/qemu-img create -F ${attrs.diskImageFormat} -b "$origImage" -f qcow2 $diskImage
     '';
 
     /* Inside the VM, run the stdenv setup script normally, but at the
diff --git a/pkgs/build-support/vm/test.nix b/pkgs/build-support/vm/test.nix
index 9074977c0edd..384c92088083 100644
--- a/pkgs/build-support/vm/test.nix
+++ b/pkgs/build-support/vm/test.nix
@@ -29,6 +29,7 @@ with vmTools;
     name = "deb-compile";
     src = patchelf.src;
     diskImage = diskImages.ubuntu1804i386;
+    diskImageFormat = "qcow2";
     memSize = 512;
     postHook = ''
       dpkg-query --list