diff --git a/repos/base-hw/src/core/spec/x86_64/pic.cc b/repos/base-hw/src/core/spec/x86_64/pic.cc
index 8d24c240fb..12c29d4e9a 100644
--- a/repos/base-hw/src/core/spec/x86_64/pic.cc
+++ b/repos/base-hw/src/core/spec/x86_64/pic.cc
@@ -170,6 +170,9 @@ Irte::access_t Ioapic::_create_irt_entry(unsigned const irq)
 
 Ioapic::Ioapic() : Mmio(Platform::mmio_to_virt(Hw::Cpu_memory_map::MMIO_IOAPIC_BASE))
 {
+	write<Ioregsel>(IOAPICVER);
+	_irte_count = read<Iowin::Maximum_redirection_entry>() + 1;
+
 	for (unsigned i = 0; i < IRQ_COUNT; i++)
 	{
 		/* set legacy/ISA IRQs to edge, high */
@@ -182,7 +185,7 @@ Ioapic::Ioapic() : Mmio(Platform::mmio_to_virt(Hw::Cpu_memory_map::MMIO_IOAPIC_B
 		}
 
 		/* remap all IRQs managed by I/O APIC */
-		if (i < IRTE_COUNT) {
+		if (i < _irte_count) {
 			Irte::access_t irte = _create_irt_entry(i);
 			write<Ioregsel>(IOREDTBL + 2 * i + 1);
 			write<Iowin>(irte >> Iowin::ACCESS_WIDTH);
@@ -198,7 +201,7 @@ void Ioapic::toggle_mask(unsigned const vector, bool const set)
 	/*
 	 * Ignore toggle requests for vectors not handled by the I/O APIC.
 	 */
-	if (vector < REMAP_BASE || vector >= REMAP_BASE + IRTE_COUNT) {
+	if (vector < REMAP_BASE || vector >= REMAP_BASE + _irte_count) {
 		return;
 	}
 
diff --git a/repos/base-hw/src/core/spec/x86_64/pic.h b/repos/base-hw/src/core/spec/x86_64/pic.h
index 595ad9f4e9..c5af1aef46 100644
--- a/repos/base-hw/src/core/spec/x86_64/pic.h
+++ b/repos/base-hw/src/core/spec/x86_64/pic.h
@@ -53,12 +53,10 @@ class Genode::Ioapic : public Mmio
 
 		enum { REMAP_BASE = Board::VECTOR_REMAP_BASE };
 
-		uint8_t _irt_count;
+		/* Number of Redirection Table entries */
+		unsigned _irte_count;
 
 		enum {
-			/* Number of Redirection Table entries */
-			IRTE_COUNT = 24,
-
 			/* Register selectors */
 			IOAPICVER = 0x01,
 			IOREDTBL  = 0x10,
@@ -130,7 +128,10 @@ class Genode::Ioapic : public Mmio
 		 */
 
 		struct Ioregsel : Register<0x00, 32> { };
-		struct Iowin    : Register<0x10, 32> { };
+		struct Iowin    : Register<0x10, 32>
+		{
+		    struct Maximum_redirection_entry : Bitfield<16, 8> { };
+		};
 };
 
 class Genode::Pic : public Mmio