diff --git a/hw/vesa.c b/hw/vesa.c
index f3c5114..d75b4b3 100644
--- a/hw/vesa.c
+++ b/hw/vesa.c
@@ -58,6 +58,9 @@
 	char *mem;
 	int r;
 
+	BUILD_BUG_ON(!is_power_of_two(VESA_MEM_SIZE));
+	BUILD_BUG_ON(VESA_MEM_SIZE < VESA_BPP/8 * VESA_WIDTH * VESA_HEIGHT);
+
 	if (!kvm->cfg.vnc && !kvm->cfg.sdl && !kvm->cfg.gtk)
 		return NULL;
 
diff --git a/include/kvm/util.h b/include/kvm/util.h
index 4ca7aa9..199724c 100644
--- a/include/kvm/util.h
+++ b/include/kvm/util.h
@@ -104,6 +104,8 @@
 	return x ? 1UL << fls_long(x - 1) : 0;
 }
 
+#define is_power_of_two(x)	((x) > 0 ? ((x) & ((x) - 1)) == 0 : 0)
+
 struct kvm;
 void *mmap_hugetlbfs(struct kvm *kvm, const char *htlbfs_path, u64 size);
 void *mmap_anon_or_hugetlbfs(struct kvm *kvm, const char *hugetlbfs_path, u64 size);
diff --git a/include/kvm/vesa.h b/include/kvm/vesa.h
index 0fac11a..e7d9713 100644
--- a/include/kvm/vesa.h
+++ b/include/kvm/vesa.h
@@ -5,8 +5,12 @@
 #define VESA_HEIGHT	480
 
 #define VESA_MEM_ADDR	0xd0000000
-#define VESA_MEM_SIZE	(4*VESA_WIDTH*VESA_HEIGHT)
 #define VESA_BPP	32
+/*
+ * We actually only need VESA_BPP/8*VESA_WIDTH*VESA_HEIGHT bytes. But the memory
+ * size must be a power of 2, so we round up.
+ */
+#define VESA_MEM_SIZE	(1 << 21)
 
 struct kvm;
 struct biosregs;
diff --git a/virtio/pci.c b/virtio/pci.c
index 99653ca..04e8018 100644
--- a/virtio/pci.c
+++ b/virtio/pci.c
@@ -435,6 +435,9 @@
 	vpci->kvm = kvm;
 	vpci->dev = dev;
 
+	BUILD_BUG_ON(!is_power_of_two(IOPORT_SIZE));
+	BUILD_BUG_ON(!is_power_of_two(PCI_IO_SIZE));
+
 	r = ioport__register(kvm, IOPORT_EMPTY, &virtio_pci__io_ops, IOPORT_SIZE, vdev);
 	if (r < 0)
 		return r;