diff --git a/debian/changelog b/debian/changelog
index 19ace9d9b..146d0c453 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,6 +1,8 @@
 linux-2.6 (2.6.36~rc7-1~experimental.1) UNRELEASED; urgency=low
 
   * New upstream release candidate
+  * qla4xxx: Fix build on some architectures lacking 64-bit I/O
+    (Closes: #598503)
 
  -- Ben Hutchings <ben@decadent.org.uk>  Thu, 07 Oct 2010 03:24:21 +0100
 
diff --git a/debian/patches/bugfix/all/qla4xxx-Fix-build-on-some-architectures-lacking-64-bit-I-O.patch b/debian/patches/bugfix/all/qla4xxx-Fix-build-on-some-architectures-lacking-64-bit-I-O.patch
new file mode 100644
index 000000000..0ddf57dd1
--- /dev/null
+++ b/debian/patches/bugfix/all/qla4xxx-Fix-build-on-some-architectures-lacking-64-bit-I-O.patch
@@ -0,0 +1,41 @@
+Subject: [PATCH] qla4xxx: Fix build on some architectures lacking 64-bit I/O
+From: Ben Hutchings <ben@decadent.org.uk>
+Date: Fri, 01 Oct 2010 04:11:07 +0100
+
+readq() and writeq() are not defined on all archictectures.  Where
+they are missing, define fallback implementations (copied from
+qla2xxx).
+
+Reference: http://bugs.debian.org/598503
+Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
+---
+ drivers/scsi/qla4xxx/ql4_nx.h |   15 +++++++++++++++
+ 1 files changed, 15 insertions(+), 0 deletions(-)
+
+diff --git a/drivers/scsi/qla4xxx/ql4_nx.h b/drivers/scsi/qla4xxx/ql4_nx.h
+index 931ad3f..85fe6cf 100644
+--- a/drivers/scsi/qla4xxx/ql4_nx.h
++++ b/drivers/scsi/qla4xxx/ql4_nx.h
+@@ -776,4 +776,19 @@ struct crb_addr_pair {
+ #define MIU_TEST_AGT_WRDATA_UPPER_LO	(0x0b0)
+ #define	MIU_TEST_AGT_WRDATA_UPPER_HI	(0x0b4)
+ 
++#ifndef readq
++static inline u64 readq(void __iomem *addr)
++{
++	return readl(addr) | (((u64) readl(addr + 4)) << 32LL);
++}
++#endif
++
++#ifndef writeq
++static inline void writeq(u64 val, void __iomem *addr)
++{
++	writel(((u32) (val)), (addr));
++	writel(((u32) (val >> 32)), (addr + 4));
++}
++#endif
++
+ #endif
+-- 
+1.7.1
+
diff --git a/debian/patches/series/base b/debian/patches/series/base
index b2b191a90..87b074729 100644
--- a/debian/patches/series/base
+++ b/debian/patches/series/base
@@ -45,3 +45,4 @@
 + bugfix/all/brcm80211-Fix-some-initialisation-failure-paths.patch
 
 + bugfix/all/vivi-Don-t-depend-on-FONTS.patch
++ bugfix/all/qla4xxx-Fix-build-on-some-architectures-lacking-64-bit-I-O.patch