diff --git a/src/vlib/pci/pci.c b/src/vlib/pci/pci.c
index dc4f382..1845a62 100644
--- a/src/vlib/pci/pci.c
+++ b/src/vlib/pci/pci.c
@@ -302,7 +302,7 @@
     [1] = "2.5", [2] = "5.0", [3] = "8.0", [4] = "16.0", [5] = "32.0"
   };
 
-  if (speed > ARRAY_LEN (speeds) || speeds[speed] == 0)
+  if (speed >= ARRAY_LEN (speeds) || speeds[speed] == 0)
     s = format (s, "unknown speed");
   else
     s = format (s, "%s GT/s", speeds[speed]);