--- a/ethtool_link_settings_test.go
+++ b/ethtool_link_settings_test.go
@@ -93,7 +93,7 @@
 
 			// Basic sanity checks if it succeeded (values might be 0 or unknown)
 			if settings.Speed == SPEED_UNKNOWN { // SPEED_UNKNOWN defined in ethtool.go
-				t.Logf("Interface '%s' reported speed as SPEED_UNKNOWN (0x%x)", intfName, SPEED_UNKNOWN)
+				t.Logf("Interface '%s' reported speed as SPEED_UNKNOWN (0x%x)", intfName, uint64(SPEED_UNKNOWN))
 			}
 		}
 	}