diff --git a/sys/powerpc/powerpc/exec_machdep.c b/sys/powerpc/powerpc/exec_machdep.c
--- a/sys/powerpc/powerpc/exec_machdep.c
+++ b/sys/powerpc/powerpc/exec_machdep.c
@@ -1083,7 +1083,7 @@
 	struct pcb *pcb;
 
 	pcb = (struct pcb *)((td->td_kstack + td->td_kstack_pages * PAGE_SIZE -
-	    sizeof(struct pcb)) & ~0x2fUL);
+	    sizeof(struct pcb)) & ~0x3fUL);
 	td->td_pcb = pcb;
 	td->td_frame = (struct trapframe *)pcb - 1;
 }
diff --git a/sys/powerpc/powerpc/vm_machdep.c b/sys/powerpc/powerpc/vm_machdep.c
--- a/sys/powerpc/powerpc/vm_machdep.c
+++ b/sys/powerpc/powerpc/vm_machdep.c
@@ -124,7 +124,7 @@
 		cpu_update_pcb(td1);
 
 	pcb = (struct pcb *)((td2->td_kstack +
-	    td2->td_kstack_pages * PAGE_SIZE - sizeof(struct pcb)) & ~0x2fUL);
+	    td2->td_kstack_pages * PAGE_SIZE - sizeof(struct pcb)) & ~0x3fUL);
 	td2->td_pcb = pcb;
 
 	/* Copy the pcb */