diff --git a/xen/arch/x86/domain_build.c b/xen/arch/x86/domain_build.c
index f858adab51..b8765be263 100644
--- a/xen/arch/x86/domain_build.c
+++ b/xen/arch/x86/domain_build.c
@@ -286,7 +286,8 @@ int construct_dom0(struct domain *d,
         nr_pages = avail_domheap_pages() + initial_images_nrpages() +
             dom0_nrpages;
     else
-        nr_pages = dom0_nrpages;
+        nr_pages = min(avail_domheap_pages() + initial_images_nrpages(),
+                       (unsigned long)dom0_nrpages);
 
     if ( (rc = parseelfimage(&dsi)) != 0 )
         return rc;
@@ -668,6 +669,8 @@ int construct_dom0(struct domain *d,
 
     if ( opt_dom0_max_vcpus == 0 )
         opt_dom0_max_vcpus = num_online_cpus();
+    if ( opt_dom0_max_vcpus > num_online_cpus() )
+        opt_dom0_max_vcpus = num_online_cpus();
     if ( opt_dom0_max_vcpus > MAX_VIRT_CPUS )
         opt_dom0_max_vcpus = MAX_VIRT_CPUS;
     printk("Dom0 has maximum %u VCPUs\n", opt_dom0_max_vcpus);