diff --git a/sim/arm/armvirt.c b/sim/arm/armvirt.c
index ba01a652ebc..c162ba79e9b 100644
--- a/sim/arm/armvirt.c
+++ b/sim/arm/armvirt.c
@@ -46,6 +46,7 @@
 
 #endif
 
+#undef PAGESIZE			/* Cleanup system headers.  */
 #define NUMPAGES 64 * 1024
 #define PAGESIZE 64 * 1024
 #define PAGEBITS 16
diff --git a/sim/bfin/dv-bfin_mmu.h b/sim/bfin/dv-bfin_mmu.h
index 2405f2818ba..408b392b686 100644
--- a/sim/bfin/dv-bfin_mmu.h
+++ b/sim/bfin/dv-bfin_mmu.h
@@ -21,6 +21,8 @@
 #ifndef DV_BFIN_MMU_H
 #define DV_BFIN_MMU_H
 
+#undef PAGE_SIZE	/* Cleanup system headers.  */
+
 void mmu_check_addr (SIM_CPU *, bu32 addr, bool write, bool inst, int size);
 void mmu_check_cache_addr (SIM_CPU *, bu32 addr, bool write, bool inst);
 void mmu_process_fault (SIM_CPU *, bu32 addr, bool write, bool inst, bool unaligned, bool miss);
diff --git a/sim/rx/mem.h b/sim/rx/mem.h
index a4c7455a20d..15bb5573fae 100644
--- a/sim/rx/mem.h
+++ b/sim/rx/mem.h
@@ -37,6 +37,8 @@ void init_mem (void);
 void mem_usage_stats (void);
 unsigned long mem_usage_cycles (void);
 
+#undef PAGE_SIZE	/* Cleanup system headers.  */
+
 /* rx_mem_ptr returns a pointer which is valid as long as the address
    requested remains within the same page.  */
 #define PAGE_BITS 12