diff --git a/hw/pci.c b/hw/pci.c
index bd65db223926c80dac19790e4e04f86ee61e2209..d63285a96ac50fc108c08e5eb7114c858bdbbe7e 100644
--- a/hw/pci.c
+++ b/hw/pci.c
@@ -193,14 +193,15 @@ int pci_bus_num(PCIBus *s)
 static int get_pci_config_device(QEMUFile *f, void *pv, size_t size)
 {
     PCIDevice *s = container_of(pv, PCIDevice, config);
-    uint8_t config[size];
+    uint8_t config[PCI_CONFIG_SPACE_SIZE];
     int i;
 
-    qemu_get_buffer(f, config, size);
-    for (i = 0; i < size; ++i)
+    assert(size == sizeof config);
+    qemu_get_buffer(f, config, sizeof config);
+    for (i = 0; i < sizeof config; ++i)
         if ((config[i] ^ s->config[i]) & s->cmask[i] & ~s->wmask[i])
             return -EINVAL;
-    memcpy(s->config, config, size);
+    memcpy(s->config, config, sizeof config);
 
     pci_update_mappings(s);