diff --git a/debian/changelog b/debian/changelog
index 1c159848233e96c0848e9cbdccd1fc6d1196c521..1720ecf3ac6d1d849423c05ceb26d58974024762 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,10 @@
+python-ppmd (0.5.0-4) UNRELEASED; urgency=medium
+
+ * Simplify 64-bit platform detection; it should be much more robust across
+ all architectures now.
+
+ -- Colin Watson <cjwatson@debian.org> Tue, 25 Mar 2025 10:03:37 +0000
+
python-ppmd (0.5.0-3) unstable; urgency=medium
* Team upload.
diff --git a/debian/patches/fix-64bit-platform-detection.patch b/debian/patches/fix-64bit-platform-detection.patch
index bb4e94c2135072ff9cb14f61e74ce52fe7ef3046..b6b1aa2007f0247c3290cf42d575bd30c77aa0c8 100644
--- a/debian/patches/fix-64bit-platform-detection.patch
+++ b/debian/patches/fix-64bit-platform-detection.patch
@@ -1,29 +1,68 @@
-From: Zixing Liu <liushuyu011@gmail.com>
-Date: Mon, 24 Mar 2025 12:36:06 +0000
+From: Colin Watson <cjwatson@debian.org>
+Date: Tue, 25 Mar 2025 09:57:01 +0000
Subject: Fix 64-bit platform detection
-MIPS and PowerPC 64-bit platform detection is not adequate.
+The typedefs in `src/ffi_build.py` need to be in sync with whether
+`PPMD_32BIT` is defined, so it's simpler to just control both using the
+same condition.
-Forwarded: not-needed
Bug-Ubuntu: https://bugs.launchpad.net/ubuntu/+source/python-ppmd/+bug/2100831
-Last-Update: 2025-03-24
+Last-Update: 2025-03-25
---
- src/ext/PpmdArch.h | 5 ++---
- 1 file changed, 2 insertions(+), 3 deletions(-)
+ src/ext/PpmdArch.h | 18 ------------------
+ src/ffi_build.py | 6 +++++-
+ 2 files changed, 5 insertions(+), 19 deletions(-)
diff --git a/src/ext/PpmdArch.h b/src/ext/PpmdArch.h
-index 678fc68..ae79c39 100644
+index 678fc68..8e991ec 100644
--- a/src/ext/PpmdArch.h
+++ b/src/ext/PpmdArch.h
-@@ -83,9 +83,8 @@ struct ISzAlloc
- || defined(__ARMEB__) \
- || defined(__THUMBEL__) \
- || defined(__THUMBEB__) \
+@@ -72,24 +72,6 @@ struct ISzAlloc
+ #define ISzAlloc_Alloc(p, size) (p)->Alloc(size)
+ #define ISzAlloc_Free(p, a) (p)->Free(a)
+
+-#if defined(_M_IX86) \
+- || defined(__i386__) \
+- || defined(_M_ARM) \
+- || defined(_M_ARM_NT) \
+- || defined(_M_ARMT) \
+- || defined(__arm__) \
+- || defined(__thumb__) \
+- || defined(__ARMEL__) \
+- || defined(__ARMEB__) \
+- || defined(__THUMBEL__) \
+- || defined(__THUMBEB__) \
- || defined(__mips__) \
- || defined(__ppc__) \
- || defined(__powerpc__) \
-+ || (defined(__mips__) && !defined(__mips64__)) \
-+ || ((defined(__ppc__) || defined(__powerpc__)) && !defined(__powerpc64__)) \
- || defined(__sparc__)
- #define PPMD_32BIT
- #endif
+- || defined(__sparc__)
+- #define PPMD_32BIT
+-#endif
+-
+ EXTERN_C_END
+
+ #endif //PPMD_CFFI_PPMDARCH_H
+diff --git a/src/ffi_build.py b/src/ffi_build.py
+index 35cd198..ad5fd48 100644
+--- a/src/ffi_build.py
++++ b/src/ffi_build.py
+@@ -221,6 +221,10 @@ int Ppmd8_DecodeSymbol(CPpmd8 *p);
+ ''')
+
+ # ---------------------------------------------------------------------------
++define_macros = []
++if not is_64bit():
++ define_macros.append(('PPMD_32BIT', None))
++
+ ffibuilder.set_source('_ppmd', r'''
+ #include "PpmdPy.h"
+
+@@ -315,7 +319,7 @@ int ppmd_decompress(CPpmd7 *p, CPpmd7z_RangeDec *rc, char *buf, int size) {
+ }
+ return size;
+ }
+-''', sources=sources, include_dirs=[src_root])
++''', sources=sources, include_dirs=[src_root], define_macros=define_macros)
+
+ if __name__ == "__main__": # not when running with setuptools
+ ffibuilder.compile(verbose=True)