diff --git a/sys/powerpc/aim/mmu_oea.c b/sys/powerpc/aim/mmu_oea.c
index ceb81d6e4dda..4aef628a0a23 100644
--- a/sys/powerpc/aim/mmu_oea.c
+++ b/sys/powerpc/aim/mmu_oea.c
@@ -921,7 +921,7 @@ moea_bootstrap(mmu_t mmup, vm_offset_t kernelstart, vm_offset_t kernelend)
 	Maxmem = powerpc_btop(phys_avail[i + 1]);
 
 	moea_cpu_bootstrap(mmup,0);
-
+	mtmsr(mfmsr() | PSL_DR | PSL_IR);
 	pmap_bootstrapped++;
 
 	/*
diff --git a/sys/powerpc/powerpc/machdep.c b/sys/powerpc/powerpc/machdep.c
index 4aa6e7f9f6d9..c6960cc38d81 100644
--- a/sys/powerpc/powerpc/machdep.c
+++ b/sys/powerpc/powerpc/machdep.c
@@ -251,6 +251,18 @@ powerpc_init(vm_offset_t fdt, vm_offset_t toc, vm_offset_t ofentry, void *mdp)
 	if (mdp == (void *)0x65504150)
 		mdp = NULL;
 
+#if AIM
+	/*
+	 * If running from an FDT, make sure we are in real mode to avoid
+	 * tromping on firmware page tables. Everything in the kernel assumes
+	 * 1:1 mappings out of firmware, so this won't break anything not
+	 * already broken. This doesn't work if there is live OF, since OF
+	 * may internally use non-1:1 mappings.
+	 */
+	if (ofentry == 0)
+		mtmsr(mfmsr() & ~(PSL_IR | PSL_DR));
+#endif
+
 	/*
 	 * Parse metadata if present and fetch parameters.  Must be done
 	 * before console is inited so cninit gets the right value of