diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index c7923bc694..167e077a1d 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -3773,7 +3773,7 @@ retry:
     if ((vm->def->ngraphics == 1) &&
         vm->def->graphics[0]->type == VIR_DOMAIN_GRAPHICS_TYPE_VNC &&
         vm->def->graphics[0]->data.vnc.autoport &&
-        vm->def->graphics[0]->data.vnc.port != -1) {
+        vm->def->graphics[0]->data.vnc.port >= QEMU_VNC_PORT_MIN) {
         if (virBitmapClearBit(driver->reservedVNCPorts,
                               vm->def->graphics[0]->data.vnc.port - \
                               QEMU_VNC_PORT_MIN) < 0) {
diff --git a/src/util/bitmap.c b/src/util/bitmap.c
index 44edb4934e..0f7e82e0ec 100644
--- a/src/util/bitmap.c
+++ b/src/util/bitmap.c
@@ -119,7 +119,7 @@ int virBitmapSetBit(virBitmapPtr bitmap, size_t b)
  */
 int virBitmapClearBit(virBitmapPtr bitmap, size_t b)
 {
-    if (b > bitmap->size - 1)
+    if (bitmap->size != 0 && b > bitmap->size - 1)
         return -1;
 
     bitmap->map[VIR_BITMAP_UNIT_OFFSET(b)] &= ~(1 << VIR_BITMAP_BIT_OFFSET(b));