--- a/base/allocator/partition_allocator/src/partition_alloc/partition_alloc_constants.h
+++ b/base/allocator/partition_allocator/src/partition_alloc/partition_alloc_constants.h
@@ -100,21 +100,21 @@
 // other constant values, we pack _all_ `PartitionRoot::Alloc` sizes perfectly
 // up against the end of a system page.
 
-#if defined(_MIPS_ARCH_LOONGSON) || defined(ARCH_CPU_LOONGARCH64)
+#if (BUILDFLAG(IS_APPLE) && defined(ARCH_CPU_64_BITS)) || \
+    defined(PARTITION_ALLOCATOR_CONSTANTS_POSIX_NONCONST_PAGE_SIZE)
 PA_ALWAYS_INLINE PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR size_t
 PartitionPageShift() {
-  return 16;  // 64 KiB
+  return PageAllocationGranularityShift() + 2;
 }
-#elif defined(ARCH_CPU_PPC64)
+#elif defined(_MIPS_ARCH_LOONGSON) || defined(ARCH_CPU_LOONGARCH64)
 PA_ALWAYS_INLINE PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR size_t
 PartitionPageShift() {
-  return 18;  // 256 KiB
+  return 16;  // 64 KiB
 }
-#elif (BUILDFLAG(IS_APPLE) && defined(ARCH_CPU_64_BITS)) || \
-    defined(PARTITION_ALLOCATOR_CONSTANTS_POSIX_NONCONST_PAGE_SIZE)
+#elif defined(ARCH_CPU_PPC64)
 PA_ALWAYS_INLINE PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR size_t
 PartitionPageShift() {
-  return PageAllocationGranularityShift() + 2;
+  return 18;  // 256 KiB
 }
 #else
 PA_ALWAYS_INLINE PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR size_t
--- a/base/allocator/partition_allocator/src/partition_alloc/page_allocator_constants.h
+++ b/base/allocator/partition_allocator/src/partition_alloc/page_allocator_constants.h
@@ -26,7 +26,8 @@
 #define PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR __attribute__((const))
 
 #elif (BUILDFLAG(IS_ANDROID) && defined(ARCH_CPU_64_BITS)) || \
-    (BUILDFLAG(IS_LINUX) && defined(ARCH_CPU_ARM64))
+    (BUILDFLAG(IS_LINUX) && defined(ARCH_CPU_ARM64)) || \
+    (BUILDFLAG(IS_LINUX) && defined(ARCH_CPU_PPC64))
 // This should work for all POSIX (if needed), but currently all other
 // supported OS/architecture combinations use either hard-coded values
 // (such as x86) or have means to determine these values without needing
@@ -86,17 +87,7 @@
 
 PA_ALWAYS_INLINE PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR size_t
 PageAllocationGranularityShift() {
-#if BUILDFLAG(IS_WIN) || defined(ARCH_CPU_PPC64)
-  // Modern ppc64 systems support 4kB (shift = 12) and 64kB (shift = 16) page
-  // sizes.  Since 64kB is the de facto standard on the platform and binaries
-  // compiled for 64kB are likely to work on 4kB systems, 64kB is a good choice
-  // here.
-  return 16;  // 64kB
-#elif defined(_MIPS_ARCH_LOONGSON) || defined(ARCH_CPU_LOONGARCH64)
-  return 14;  // 16kB
-#elif BUILDFLAG(IS_APPLE) && defined(ARCH_CPU_64_BITS)
-  return static_cast<size_t>(vm_page_shift);
-#elif defined(PARTITION_ALLOCATOR_CONSTANTS_POSIX_NONCONST_PAGE_SIZE)
+#if defined(PARTITION_ALLOCATOR_CONSTANTS_POSIX_NONCONST_PAGE_SIZE)
   // arm64 supports 4kb (shift = 12), 16kb (shift = 14), and 64kb (shift = 16)
   // page sizes. Retrieve from or initialize cache.
   size_t shift = page_characteristics.shift.load(std::memory_order_relaxed);
@@ -106,6 +97,16 @@
     page_characteristics.shift.store(shift, std::memory_order_relaxed);
   }
   return shift;
+#elif BUILDFLAG(IS_WIN) || defined(ARCH_CPU_PPC64)
+  // Modern ppc64 systems support 4kB (shift = 12) and 64kB (shift = 16) page
+  // sizes.  Since 64kB is the de facto standard on the platform and binaries
+  // compiled for 64kB are likely to work on 4kB systems, 64kB is a good choice
+  // here.
+  return 16;  // 64kB
+#elif defined(_MIPS_ARCH_LOONGSON) || defined(ARCH_CPU_LOONGARCH64)
+  return 14;  // 16kB
+#elif BUILDFLAG(IS_APPLE) && defined(ARCH_CPU_64_BITS)
+  return static_cast<size_t>(vm_page_shift);
 #else
   return 12;  // 4kB
 #endif
--- a/base/allocator/partition_allocator/src/partition_alloc/address_space_randomization.h
+++ b/base/allocator/partition_allocator/src/partition_alloc/address_space_randomization.h
@@ -180,10 +180,10 @@
       #else  // !BUILDFLAG(IS_AIX) && !defined(ARCH_CPU_BIG_ENDIAN)
 
         // Little-endian Linux PPC has 48 bits of virtual addressing. Use 46.
-        PA_ALWAYS_INLINE constexpr uintptr_t ASLRMask() {
+        PA_ALWAYS_INLINE PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR uintptr_t ASLRMask() {
           return AslrMask(46);
         }
-        PA_ALWAYS_INLINE constexpr uintptr_t ASLROffset() {
+        PA_ALWAYS_INLINE PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR uintptr_t ASLROffset() {
           return AslrAddress(0);
         }
 
--- a/base/allocator/partition_allocator/src/partition_alloc/partition_page_constants.h
+++ b/base/allocator/partition_allocator/src/partition_alloc/partition_page_constants.h
@@ -17,10 +17,15 @@
 // PartitionPageSize() is 4 times the OS page size.
 static constexpr size_t kMaxSlotsPerSlotSpan = 4 * (1 << 14) / kSmallestBucket;
 #elif defined(PARTITION_ALLOCATOR_CONSTANTS_POSIX_NONCONST_PAGE_SIZE)
+#if defined(ARCH_CPU_PPC64)
+// System page size can be 4 or 64 kiB on Linux on ppc64.  Use 64 kiB maximum.
+static constexpr size_t kMaxSlotsPerSlotSpan = 4 * (1 << 16) / kSmallestBucket;
+#else
 // System page size can be 4, 16, or 64 kiB on Linux on arm64. 64 kiB is
 // currently (kMaxSlotsPerSlotSpanBits == 13) not supported by the code,
 // so we use the 16 kiB maximum (64 kiB will crash).
 static constexpr size_t kMaxSlotsPerSlotSpan = 4 * (1 << 14) / kSmallestBucket;
+#endif
 #elif BUILDFLAG(IS_LINUX) && defined(ARCH_CPU_PPC64)
 // System page size is not a constant on OpenPOWER systems, but is either 4kiB
 // or 64kiB (1 << 12 or 1 << 16)