diff --git a/netbox/netbox.go b/netbox/netbox.go
index 6889eb6..03a4401 100644
--- a/netbox/netbox.go
+++ b/netbox/netbox.go
@@ -189,7 +189,7 @@ func (a *Allocator) AllocCIDR() (cidr string, err error) {
 		return
 	}
 	defer resp.Body.Close()
-	if resp.StatusCode == http.StatusNoContent {
+	if resp.StatusCode == http.StatusConflict {
 		return "", netalloc.ErrPrefixFull
 	}
 	if resp.StatusCode == http.StatusCreated {