diff --git a/share/ppc.tmpl b/share/ppc.tmpl
index 8ec2946c..52ed197c 100644
--- a/share/ppc.tmpl
+++ b/share/ppc.tmpl
@@ -16,7 +16,7 @@ macboot = ""
 %>
 
 mkdir images
-install ${runtime} images
+install ${runtime_img} images
 
 mkdir ${BOOTDIR} ${BOOTDIR}/chrp etc
 install ${ANABOOTDIR}/bootinfo.txt ${BOOTDIR}
diff --git a/share/s390.tmpl b/share/s390.tmpl
index c58f8d46..8ab4621c 100644
--- a/share/s390.tmpl
+++ b/share/s390.tmpl
@@ -9,7 +9,7 @@ kernel = kernels[0]
 %>
 
 mkdir images
-install ${runtime} images
+install ${runtime_img} images
 
 install ${ANABOOTDIR}/redhat.exec ${BOOTDIR}
 install ${ANABOOTDIR}/generic.prm ${BOOTDIR}
diff --git a/share/sparc.tmpl b/share/sparc.tmpl
index faeff017..858995a9 100644
--- a/share/sparc.tmpl
+++ b/share/sparc.tmpl
@@ -5,7 +5,7 @@ KERNELDIR=BOOTDIR
 %>
 
 mkdir images
-install ${runtime} images
+install ${runtime_img} images
 
 install boot/*.b ${BOOTDIR}
 install ${ANABOOTDIR}/silo.conf ${BOOTDIR}
@@ -26,5 +26,5 @@ runcmd mkisofs -R -J -T -G /${BOOTDIR}/isofs.b -B ... \
   -sparc-label "${product.name} ${product.version} Boot Disc" \
   -o ${outroot}/images/boot.iso \
   -graft-points boot=${outroot}/${BOOTDIR} \
-                ${runtime}=${outroot}/${runtime}
+                ${runtime_img}=${outroot}/${runtime_img}
 treeinfo images-${basearch} boot.iso images/boot.iso
diff --git a/share/x86.tmpl b/share/x86.tmpl
index c43a9787..d6184a8a 100644
--- a/share/x86.tmpl
+++ b/share/x86.tmpl
@@ -7,7 +7,7 @@ KERNELDIR=PXEBOOTDIR
 %>
 
 mkdir images
-install ${runtime} images
+install ${runtime_img} images
 
 mkdir ${BOOTDIR} ${KERNELDIR}
 install ${SYSLINUXDIR}/isolinux.bin ${BOOTDIR}
@@ -66,7 +66,7 @@ runcmd mkisofs -o ${outroot}/images/boot.iso \
        ${efiargs} -R -J -V '${product.name}' -T -graft-points \
        ${BOOTDIR}=${outroot}/${BOOTDIR} \
        ${KERNELDIR}=${outroot}/${KERNELDIR} \
-       ${runtime}=${outroot}/${runtime} \
+       ${runtime_img}=${outroot}/${runtime_img} \
        ${efigraft}
 runcmd isohybrid ${outroot}/images/boot.iso
 treeinfo images-${basearch} boot.iso images/boot.iso
diff --git a/src/pylorax/treebuilder.py b/src/pylorax/treebuilder.py
index ad155bc4..28414f6f 100644
--- a/src/pylorax/treebuilder.py
+++ b/src/pylorax/treebuilder.py
@@ -143,8 +143,10 @@ class TreeBuilder(object):
     '''Builds the arch-specific boot images.
     inroot should be the installtree root (the newly-built runtime dir)'''
     def __init__(self, product, arch, inroot, outroot, runtime, templatedir=None):
+        # NOTE: if you pass an arg named "runtime" to a mako template it'll
+        # clobber some mako internal variables - hence "runtime_img".
         v = DataHolder(arch=arch, product=product,
-                       inroot=inroot, outroot=outroot, runtime=runtime,
+                       inroot=inroot, outroot=outroot, runtime_img=runtime,
                        basearch=arch.basearch, libdir=arch.libdir,
                        exists = lambda p: _exists(p, root=inroot))
         self.vars = v