diff --git a/kernel.go b/kernel.go
index 52b530e..956a835 100644
--- a/kernel.go
+++ b/kernel.go
@@ -306,7 +306,7 @@ func generateBaseDockerImage(registry string, commands []config.DockerCommand,
 		d += "RUN apt-get install -y build-essential libelf-dev\n"
 		d += "RUN apt-get install -y wget git\n"
 		// Install a single kernel and headers to ensure all dependencies are cached
-		d += "RUN PKGNAME=$(apt-cache search --names-only '^linux-headers-[0-9\\.\\-]*-generic' | awk '{ print $1 }' | head -n 1) " +
+		d += "RUN export PKGNAME=$(apt-cache search --names-only '^linux-headers-[0-9\\.\\-]*-generic' | awk '{ print $1 }' | head -n 1); " +
 			"apt-get install -y $PKGNAME $(echo $PKGNAME | sed 's/headers/image/')\n"
 		if sk.DistroRelease >= "14.04" {
 			d += "RUN apt-get install -y libseccomp-dev\n"