diff --git a/build b/build
index 14c4eb4..050f3ff 100755
--- a/build
+++ b/build
@@ -133,6 +133,8 @@ name_to_component_map = {
             'protobuf-compiler',
             'python-dev',
             'python-pip',
+            # For prebuilt qcow2 unpack.
+            'qemu-utils',
             'scons',
             'zlib1g-dev',
         },
diff --git a/common.py b/common.py
index 3b0f933..a591b89 100644
--- a/common.py
+++ b/common.py
@@ -537,7 +537,7 @@ def print_time(ellapsed_seconds):
     print("time {:02}:{:02}:{:02}".format(int(hours), int(minutes), int(seconds)))
 
 def raw_to_qcow2(prebuilt=False, reverse=False):
-    if prebuilt:
+    if prebuilt or not os.path.exists(common.qemu_img_executable):
         disable_trace = []
         qemu_img_executable = common.qemu_img_basename
     else:
diff --git a/run b/run
index 24c4494..1962aa6 100755
--- a/run
+++ b/run
@@ -249,13 +249,14 @@ def main(args, extra_args=None):
                 raise_image_not_found()
             extra_emulator_args.extend(extra_qemu_args)
             common.make_run_dirs()
-            if args.prebuilt:
+            if args.prebuilt or not os.path.exists(common.qemu_executable):
                 qemu_executable = common.qemu_executable_basename
-                qemu_found = shutil.which(qemu_executable) is not None
+                qemu_executable_prebuilt = True
             else:
                 qemu_executable = common.qemu_executable
-                qemu_found = os.path.exists(qemu_executable)
-            if not qemu_found and not args.dry_run:
+                qemu_executable_prebuilt = False
+            qemu_executable = shutil.which(qemu_executable)
+            if qemu_executable is None:
                 raise Exception('QEMU executable not found, did you forget to build or install it?\n' \
                                 'Tried to use: ' + qemu_executable)
             if args.debug_vm:
@@ -296,10 +297,11 @@ def main(args, extra_args=None):
                     '-smp', str(args.cpus), common.Newline,
                 ] +
                 virtfs_cmd +
-                qemu_user_and_system_options +
                 serial_monitor +
                 vnc
             )
+            if not qemu_executable_prebuilt:
+                cmd.extend(qemu_user_and_system_options)
             if args.initrd:
                 extra_emulator_args.extend(['-initrd', os.path.join(common.buildroot_images_dir, 'rootfs.cpio')])
             rr = args.record or args.replay