--- old/src/os_cpu/aix_ppc/vm/os_aix_ppc.cpp	2016-12-02 11:44:53.221292000 +0100
+++ new/src/os_cpu/aix_ppc/vm/os_aix_ppc.cpp	2016-12-02 11:44:53.070283000 +0100
@@ -535,11 +535,11 @@
 ////////////////////////////////////////////////////////////////////////////////
 // thread stack
 
-// These sizes exclude libc stack guard pages, but include
-// the HotSpot guard pages.
-size_t os::Posix::_compiler_thread_min_stack_allowed = 512 * K;
-size_t os::Posix::_java_thread_min_stack_allowed = 512 * K;
-size_t os::Posix::_vm_internal_thread_min_stack_allowed = 128 * K;
+// Minimum usable stack sizes required to get to user code. Space for
+// HotSpotguard pages is added later.
+size_t os::Posix::_compiler_thread_min_stack_allowed = 192 * K;
+size_t os::Posix::_java_thread_min_stack_allowed = 64 * K;
+size_t os::Posix::_vm_internal_thread_min_stack_allowed = 64 * K;
 
 // Return default stack size for thr_type.
 size_t os::Posix::default_stack_size(os::ThreadType thr_type) {