diff --git a/src/system/kernel/arch/x86/irq_routing_table.cpp b/src/system/kernel/arch/x86/irq_routing_table.cpp
index c442fac456..578896baef 100644
--- a/src/system/kernel/arch/x86/irq_routing_table.cpp
+++ b/src/system/kernel/arch/x86/irq_routing_table.cpp
@@ -578,8 +578,11 @@ ensure_all_functions_matched(pci_module_info* pci, uint8 bus,
 			}
 
 			if (!matched) {
-				if (pci->read_pci_config(bus, device, function,
-						PCI_interrupt_line, 1) == 0) {
+				uint32 interrupt_line = pci->read_pci_config(bus, device,
+					function, PCI_interrupt_line, 1);
+				// On x86, interrupt line 255 means "unknown" or "no connection"
+				// (PCI Local Bus spec 3.0, section 6.2.4 / page 223, footnote.)
+				if (interrupt_line == 0 || interrupt_line == 255) {
 					dprintf("assuming no interrupt use on PCI device"
 						" %u:%u:%u (bios irq 0, no routing information)\n",
 						bus, device, function);