diff --git a/kernel/disk/ahci/hba.cpp b/kernel/disk/ahci/hba.cpp
index e35f86da..5d4c4062 100644
--- a/kernel/disk/ahci/hba.cpp
+++ b/kernel/disk/ahci/hba.cpp
@@ -126,6 +126,13 @@ void HBA__OnInterrupt(struct interrupt_context*, void* context)
 
 bool HBA::Initialize(Ref<Descriptor> dev, const char* devpath)
 {
+	interrupt_index = PCI::SetupInterruptLine(devaddr);
+	if ( !interrupt_index )
+	{
+		LogF("error: cannot determine interrupt line");
+		return errno = EINVAL, false;
+	}
+
 	pcibar_t mmio_bar = PCI::GetBAR(devaddr, 5);
 	if ( mmio_bar.size() < sizeof(struct hba_regs) && /* or || ? */
 	     mmio_bar.size() < 1024 )
@@ -228,8 +235,6 @@ bool HBA::Initialize(Ref<Descriptor> dev, const char* devpath)
 		}
 	}
 
-	interrupt_index =
-		Interrupt::IRQ0 + PCI::Read8(devaddr, PCIFIELD_INTERRUPT_LINE);
 	interrupt_registration.handler = HBA__OnInterrupt;
 	interrupt_registration.context = this;
 	Interrupt::RegisterHandler(interrupt_index, &interrupt_registration);
diff --git a/kernel/disk/ahci/hba.h b/kernel/disk/ahci/hba.h
index 6da4c5b9..e94f7550 100644
--- a/kernel/disk/ahci/hba.h
+++ b/kernel/disk/ahci/hba.h
@@ -56,7 +56,7 @@ private:
 	addralloc_t mmio_alloc;
 	volatile struct hba_regs* regs;
 	uint32_t devaddr;
-	unsigned int interrupt_index;
+	uint8_t interrupt_index;
 	bool interrupt_registered;
 	bool mmio_alloced;
 
diff --git a/kernel/disk/ata/hba.cpp b/kernel/disk/ata/hba.cpp
index 62912c5c..0cb52a76 100644
--- a/kernel/disk/ata/hba.cpp
+++ b/kernel/disk/ata/hba.cpp
@@ -147,7 +147,7 @@ void FixDefaultDeviceBars(pcibar_t* basebar, pcibar_t* ctrlbar, uint8_t* irq,
 	bool compatibility = interface == 0x00 || interface == 0x02;
 
 	if ( compatibility )
-		*irq = channel_index == 0 ? 14 : 15;
+		*irq = channel_index == 0 ? Interrupt::IRQ14 : Interrupt::IRQ15;
 
 	if ( compatibility ||
 	     basebar->addr_raw == 0 ||
@@ -175,8 +175,14 @@ bool Channel::Initialize(Ref<Descriptor> dev, const char* devpath)
 	pcibar_t basebar = PCI::GetBAR(devaddr, 2 * channel_index + 0);
 	pcibar_t ctrlbar = PCI::GetBAR(devaddr, 2 * channel_index + 1);
 	pcibar_t busmasterbar = PCI::GetBAR(devaddr, 4);
-	uint8_t irq = PCI::Read8(devaddr, PCIFIELD_INTERRUPT_LINE);
-	FixDefaultDeviceBars(&basebar, &ctrlbar, &irq, channel_index, interface);
+	interrupt_index = PCI::SetupInterruptLine(devaddr);
+	FixDefaultDeviceBars(&basebar, &ctrlbar, &interrupt_index, channel_index, interface);
+
+	if ( !interrupt_index )
+	{
+		LogF("error: cannot determine interrupt line");
+		return errno = EINVAL, false;
+	}
 
 	if ( !basebar.is_iospace() )
 	{
@@ -255,8 +261,6 @@ bool Channel::Initialize(Ref<Descriptor> dev, const char* devpath)
 		}
 	}
 
-	interrupt_index = Interrupt::IRQ0 + irq;
-
 	interrupt_registration.handler = Channel__OnInterrupt;
 	interrupt_registration.context = this;
 	Interrupt::RegisterHandler(interrupt_index, &interrupt_registration);
diff --git a/kernel/disk/ata/hba.h b/kernel/disk/ata/hba.h
index 81eaf418..c7620555 100644
--- a/kernel/disk/ata/hba.h
+++ b/kernel/disk/ata/hba.h
@@ -61,7 +61,7 @@ private:
 	uint16_t port_control;
 	uint16_t busmaster_base;
 	Port* drives[2];
-	unsigned int interrupt_index;
+	uint8_t interrupt_index;
 	bool interrupt_registered;
 
 };
diff --git a/kernel/include/sortix/kernel/pci.h b/kernel/include/sortix/kernel/pci.h
index 17d2e76d..edc2d034 100644
--- a/kernel/include/sortix/kernel/pci.h
+++ b/kernel/include/sortix/kernel/pci.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011, 2012, 2013, 2014, 2015 Jonas 'Sortie' Termansen.
+ * Copyright (c) 2011, 2012, 2013, 2014, 2015, 2016 Jonas 'Sortie' Termansen.
  *
  * Permission to use, copy, modify, and distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
@@ -152,6 +152,7 @@ pcibar_t GetExpansionROM(uint32_t devaddr);
 void EnableExpansionROM(uint32_t devaddr);
 void DisableExpansionROM(uint32_t devaddr);
 bool IsExpansionROMEnabled(uint32_t devaddr);
+uint8_t SetupInterruptLine(uint32_t devaddr);
 
 } // namespace PCI
 } // namespace Sortix
diff --git a/kernel/pci.cpp b/kernel/pci.cpp
index b380f5ee..758daa82 100644
--- a/kernel/pci.cpp
+++ b/kernel/pci.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011, 2012, 2013, 2014 Jonas 'Sortie' Termansen.
+ * Copyright (c) 2011, 2012, 2013, 2014, 2015, 2016 Jonas 'Sortie' Termansen.
  *
  * Permission to use, copy, modify, and distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
@@ -21,6 +21,7 @@
 #include <endian.h>
 
 #include <sortix/kernel/cpu.h>
+#include <sortix/kernel/interrupt.h>
 #include <sortix/kernel/ioport.h>
 #include <sortix/kernel/kernel.h>
 #include <sortix/kernel/kthread.h>
@@ -31,8 +32,8 @@ namespace PCI {
 
 static kthread_mutex_t pci_lock = KTHREAD_MUTEX_INITIALIZER;
 
-const uint16_t CONFIG_ADDRESS = 0xCF8;
-const uint16_t CONFIG_DATA = 0xCFC;
+static const uint16_t CONFIG_ADDRESS = 0xCF8;
+static const uint16_t CONFIG_DATA = 0xCFC;
 
 uint32_t MakeDevAddr(uint8_t bus, uint8_t slot, uint8_t func)
 {
@@ -279,6 +280,26 @@ bool IsExpansionROMEnabled(uint32_t devaddr)
 	return PCI::Read32(devaddr, 0x30) & 0x1;
 }
 
+static bool IsOkayInterruptLine(uint8_t line)
+{
+	if ( line == 0 )
+		return false; // Conflict with PIT.
+	if ( line == 2 )
+		return false; // Cascade, can't be received.
+	if ( 16 <= line )
+		return false; // Not in set of valid IRQs.
+	return true;
+}
+
+uint8_t SetupInterruptLine(uint32_t devaddr)
+{
+	ScopedLock lock(&pci_lock);
+	uint8_t line = Read8(devaddr, PCIFIELD_INTERRUPT_LINE);
+	if ( !IsOkayInterruptLine(line) )
+		return 0;
+	return Interrupt::IRQ0 + line;
+}
+
 void Init()
 {
 }