diff --git a/lib/libpt/pt.asm b/lib/libpt/pt.asm
index a329120f..ee56f06c 100644
--- a/lib/libpt/pt.asm
+++ b/lib/libpt/pt.asm
@@ -17,7 +17,7 @@ _PtPatternPos   set     mt_data+mt_PatternPos
 _PtInstallCIA:
         movem.l d2-d7/a2-a6,-(sp)
         st.b    d0
-        suba.l  a0,a0
+        move.l  _ExcVecBase,a0
         lea     $dff000,a6
         bsr     _mt_install_cia
         movem.l (sp)+,d2-d7/a2-a6
diff --git a/system/kernel/memory.c b/system/kernel/memory.c
index d565827c..26213032 100644
--- a/system/kernel/memory.c
+++ b/system/kernel/memory.c
@@ -199,6 +199,7 @@ void AddMemory(void *ptr, u_int size, u_int attributes) {
   u_int sz = (uintptr_t)end - (uintptr_t)ar->start;
   WordT *bt = ar->start;
 
+  Assume(ar != NULL);
   Assume(end > (void *)ar->start + FREEBLK_SZ);
 
   ar->succ = NULL;
diff --git a/system/loader.c b/system/loader.c
index e56c05d6..82764b96 100644
--- a/system/loader.c
+++ b/system/loader.c
@@ -41,7 +41,8 @@ void Loader(BootDataT *bd) {
 
     for (i = 0; i < bd->bd_nregions; i++) {
       MemRegionT *mr = &bd->bd_region[i];
-      AddMemory((void *)mr->mr_lower, mr->mr_upper - mr->mr_lower, mr->mr_attr);
+      uintptr_t lower = mr->mr_lower ? mr->mr_lower : 1;
+      AddMemory((void *)lower, mr->mr_upper - lower, mr->mr_attr);
     }
   }