diff --git a/Makefile-rpm-ostree.am b/Makefile-rpm-ostree.am
index 29c35537..fab0e5c5 100644
--- a/Makefile-rpm-ostree.am
+++ b/Makefile-rpm-ostree.am
@@ -51,7 +51,7 @@ rpm_ostree_SOURCES = src/app/main.cxx \
 	src/app/rpmostree-dbus-helpers.h \
 	src/app/rpmostree-override-builtins.h \
 	src/app/rpmostree-override-builtins.c \
-	src/app/rpmostree-libbuiltin.c \
+	src/app/rpmostree-libbuiltin.cxx \
 	src/app/rpmostree-libbuiltin.h \
 	src/app/rpmostree-polkit-agent.c \
 	src/app/rpmostree-polkit-agent.h \
diff --git a/src/app/rpmostree-libbuiltin.c b/src/app/rpmostree-libbuiltin.cxx
similarity index 98%
rename from src/app/rpmostree-libbuiltin.c
rename to src/app/rpmostree-libbuiltin.cxx
index baef4d94..6ceccab9 100644
--- a/src/app/rpmostree-libbuiltin.c
+++ b/src/app/rpmostree-libbuiltin.cxx
@@ -99,7 +99,7 @@ rpmostree_print_treepkg_diff_from_sysroot_path (const gchar   *sysroot_path,
   g_autoptr(GPtrArray) deployments = ostree_sysroot_get_deployments (sysroot);
   g_assert_cmpuint (deployments->len, >, 1);
 
-  OstreeDeployment *new_deployment = deployments->pdata[0];
+  auto new_deployment = static_cast<OstreeDeployment *>(deployments->pdata[0]);
   OstreeDeployment *booted_deployment = ostree_sysroot_get_booted_deployment (sysroot);
 
   if (!booted_deployment || ostree_deployment_equal (booted_deployment, new_deployment))