diff --git a/tools/ocaml/libs/xc/xenctrl_stubs.c b/tools/ocaml/libs/xc/xenctrl_stubs.c
index f5cf0edb24..c27c897e66 100644
--- a/tools/ocaml/libs/xc/xenctrl_stubs.c
+++ b/tools/ocaml/libs/xc/xenctrl_stubs.c
@@ -455,6 +455,9 @@ CAMLprim value stub_xc_vcpu_getaffinity(value xch, value domid,
 	int i, len = xc_get_max_cpus(_H(xch));
 	int retval;
 
+	if (len < 1)
+		failwith_xc(_H(xch));
+
 	c_cpumap = xc_cpumap_alloc(_H(xch));
 	if (c_cpumap == NULL)
 		failwith_xc(_H(xch));
@@ -805,6 +808,12 @@ CAMLprim value stub_xc_version_version(value xch)
 
 	caml_enter_blocking_section();
 	packed = xc_version(_H(xch), XENVER_version, NULL);
+	caml_leave_blocking_section();
+
+	if (packed < 0)
+		failwith_xc(_H(xch));
+
+	caml_enter_blocking_section();
 	retval = xc_version(_H(xch), XENVER_extraversion, &extra);
 	caml_leave_blocking_section();