diff --git a/build/toolchain.gypi b/build/toolchain.gypi
index b8c7317785..f1f46c89c7 100644
--- a/build/toolchain.gypi
+++ b/build/toolchain.gypi
@@ -1144,6 +1144,11 @@
           }],
           ['OS=="aix"', {
             'ldflags': [ '-Wl,-bbigtoc' ],
+            'conditions': [
+              ['v8_target_arch=="ppc64"', {
+                'cflags': [ '-maix64 -mcmodel=large' ],
+              }],
+            ],
           }],
           ['OS=="android"', {
             'variables': {
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 1c11163c75..bb1bc43d1b 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -2899,7 +2899,7 @@ AllocationResult Heap::AllocatePropertyCell() {
 AllocationResult Heap::AllocateWeakCell(HeapObject* value) {
   int size = WeakCell::kSize;
   STATIC_ASSERT(WeakCell::kSize <= Page::kMaxRegularHeapObjectSize);
-  HeapObject* result;
+  HeapObject* result = NULL;
   {
     AllocationResult allocation =
         AllocateRaw(size, OLD_POINTER_SPACE, OLD_POINTER_SPACE);
@@ -4474,7 +4474,7 @@ AllocationResult Heap::AllocateExtendedConstantPoolArray(
 AllocationResult Heap::AllocateEmptyConstantPoolArray() {
   ConstantPoolArray::NumberOfEntries small(0, 0, 0, 0);
   int size = ConstantPoolArray::SizeFor(small);
-  HeapObject* result;
+  HeapObject* result = NULL;
   {
     AllocationResult allocation =
         AllocateRaw(size, OLD_DATA_SPACE, OLD_DATA_SPACE);
@@ -4490,7 +4490,7 @@ AllocationResult Heap::AllocateSymbol() {
   // Statically ensure that it is safe to allocate symbols in paged spaces.
   STATIC_ASSERT(Symbol::kSize <= Page::kMaxRegularHeapObjectSize);
 
-  HeapObject* result;
+  HeapObject* result = NULL;
   AllocationResult allocation =
       AllocateRaw(Symbol::kSize, OLD_POINTER_SPACE, OLD_POINTER_SPACE);
   if (!allocation.To(&result)) return allocation;
diff --git a/src/heap/mark-compact.cc b/src/heap/mark-compact.cc
index f0483c9561..c48a95429f 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -2877,11 +2877,13 @@ class PointersUpdatingVisitor : public ObjectVisitor {
 
 // TODO(ishell): remove, once crbug/454297 is caught.
 #if V8_TARGET_ARCH_64_BIT
+#ifndef V8_OS_AIX  // no point checking on AIX as full 64 range is supported
     const uintptr_t kBoundary = V8_UINT64_C(1) << 48;
     STATIC_ASSERT(kBoundary > 0);
     if (reinterpret_cast<uintptr_t>(heap_obj->address()) >= kBoundary) {
       CheckLayoutDescriptorAndDie(heap, slot);
     }
+#endif
 #endif
     MapWord map_word = heap_obj->map_word();
     if (map_word.IsForwardingAddress()) {
diff --git a/test/cctest/cctest.gyp b/test/cctest/cctest.gyp
index e78d0b70d5..3f7d56aa43 100644
--- a/test/cctest/cctest.gyp
+++ b/test/cctest/cctest.gyp
@@ -272,6 +272,9 @@
             },
           },
         }],
+        ['OS=="aix"', {
+          'ldflags': [ '-Wl,-bbigtoc' ],
+        }],
         ['component=="shared_library"', {
           # cctest can't be built against a shared library, so we need to
           # depend on the underlying static target in that case.