diff --git a/compiler-rt/lib/asan/asan_allocator.h b/compiler-rt/lib/asan/asan_allocator.h
index 247d8bb77c984..7dfb055c4f4b7 100644
--- a/compiler-rt/lib/asan/asan_allocator.h
+++ b/compiler-rt/lib/asan/asan_allocator.h
@@ -198,7 +198,11 @@ const uptr kAllocatorSpace = ~(uptr)0;
 #    endif  // SANITIZER_APPLE
 
 #    if defined(__powerpc64__)
+#      if SANITIZER_AIX
+const uptr kAllocatorSize = 1ULL << 38;  // 256G.
+#      else
 const uptr kAllocatorSize  =  0x20000000000ULL;  // 2T.
+#      endif
 typedef DefaultSizeClassMap SizeClassMap;
 #    elif defined(__aarch64__) && SANITIZER_ANDROID
 // Android needs to support 39, 42 and 48 bit VMA.
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_allocator_primary32.h b/compiler-rt/lib/sanitizer_common/sanitizer_allocator_primary32.h
index 602b197c42ae3..0faf9b3c151a4 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_allocator_primary32.h
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_allocator_primary32.h
@@ -288,6 +288,7 @@ class SizeClassAllocator32 {
   uptr ComputeRegionId(uptr mem) const {
     if (SANITIZER_SIGN_EXTENDED_ADDRESSES)
       mem &= (kSpaceSize - 1);
+    mem -= kSpaceBeg;
     const uptr res = mem >> kRegionSizeLog;
     CHECK_LT(res, kNumPossibleRegions);
     return res;
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_platform.h b/compiler-rt/lib/sanitizer_common/sanitizer_platform.h
index 196c0a988478e..71bc80e87e3f7 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_platform.h
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_platform.h
@@ -319,7 +319,11 @@
 #endif
 
 // The first address that can be returned by mmap.
-#define SANITIZER_MMAP_BEGIN 0
+#if SANITIZER_AIX && SANITIZER_WORDSIZE == 64
+#  define SANITIZER_MMAP_BEGIN 0x0a00000000000000ULL
+#else
+#  define SANITIZER_MMAP_BEGIN 0
+#endif
 
 // The range of addresses which can be returned my mmap.
 // FIXME: this value should be different on different platforms.  Larger values