diff --git a/config.h.in b/config.h.in
index df662fb..c4270d1 100644
--- a/config.h.in
+++ b/config.h.in
@@ -3,6 +3,9 @@
 /* adds support for libffi */
 #undef ENABLE_LIBFFI
 
+/* use flat segment and dirty vectors (not used yet) */
+#undef FLAT_TABLES
+
 /* Define to 1 if you have the <assert.h> header file. */
 #undef HAVE_ASSERT_H
 
diff --git a/configure b/configure
index 695d1de..a887a32 100755
--- a/configure
+++ b/configure
@@ -5606,6 +5606,14 @@ cat >>confdefs.h <<_ACEOF
 _ACEOF
 
 
+if test "$ac_cv_sizeof_void_p" = 4; then
+
+cat >>confdefs.h <<\_ACEOF
+#define FLAT_TABLES 1
+_ACEOF
+
+fi
+
 
 # Checks for libraries.
 { $as_echo "$as_me:$LINENO: checking for library containing dlsym" >&5
diff --git a/configure.ac b/configure.ac
index 9034ff2..bcfbaff 100644
--- a/configure.ac
+++ b/configure.ac
@@ -29,6 +29,11 @@ case "$target_os" in
   esac
 
 AC_CHECK_SIZEOF(void *)
+if test "$ac_cv_sizeof_void_p" = 4; then
+   AC_DEFINE(FLAT_TABLES, 1, 
+     [use flat segment and dirty vectors (not used yet)])
+fi
+
 
 # Checks for libraries.
 AC_SEARCH_LIBS(dlsym, dl,, [AC_MSG_ERROR([Cannot find libdl])])
diff --git a/src/ikarus-data.h b/src/ikarus-data.h
index 08e0237..b625b2d 100644
--- a/src/ikarus-data.h
+++ b/src/ikarus-data.h
@@ -190,14 +190,14 @@ void ikarus_usage_short(void);
 void* ik_malloc(int);
 void ik_free(void*, int);
 
-ikptr ik_mmap(int);
-ikptr ik_mmap_typed(int size, unsigned int type, ikpcb*);
-ikptr ik_mmap_ptr(int size, int gen, ikpcb*);
-ikptr ik_mmap_data(int size, int gen, ikpcb*);
-ikptr ik_mmap_code(int size, int gen, ikpcb*);
-ikptr ik_mmap_mixed(int size, ikpcb*);
-void ik_munmap(ikptr, int);
-void ik_munmap_from_segment(ikptr, unsigned long int, ikpcb*);
+ikptr ik_mmap(long int);
+ikptr ik_mmap_typed(long int size, unsigned int type, ikpcb*);
+ikptr ik_mmap_ptr(long int size, int gen, ikpcb*);
+ikptr ik_mmap_data(long int size, int gen, ikpcb*);
+ikptr ik_mmap_code(long int size, int gen, ikpcb*);
+ikptr ik_mmap_mixed(long int size, ikpcb*);
+void ik_munmap(ikptr, long int);
+void ik_munmap_from_segment(ikptr, long int, ikpcb*);
 ikpcb* ik_make_pcb();
 void ik_delete_pcb(ikpcb*);
 void ik_free_symbol_table(ikpcb* pcb);
diff --git a/src/ikarus-runtime.c b/src/ikarus-runtime.c
index 2c7082a..4be15c6 100644
--- a/src/ikarus-runtime.c
+++ b/src/ikarus-runtime.c
@@ -50,8 +50,8 @@ extern char **environ;
 #define segment_shift (pageshift+pageshift-2)
 #define segment_index(x) (((unsigned long int)(x)) >> segment_shift)
 
-ikptr ik_mmap(int size);
-void ik_munmap(ikptr mem, int size);
+ikptr ik_mmap(long int size);
+void ik_munmap(ikptr mem, long int size);
 
 static void
 extend_table_maybe(ikptr p, unsigned long int size, ikpcb* pcb){
@@ -120,7 +120,7 @@ set_segment_type(ikptr base, unsigned long int size, unsigned int type, ikpcb* p
 }
 
 void
-ik_munmap_from_segment(ikptr base, unsigned long int size, ikpcb* pcb){
+ik_munmap_from_segment(ikptr base, long int size, ikpcb* pcb){
   assert(base >= pcb->memory_base);
   assert((base+size) <= pcb->memory_end);
   assert(size == align_to_next_page(size));
@@ -158,7 +158,7 @@ ik_munmap_from_segment(ikptr base, unsigned long int size, ikpcb* pcb){
 
 
 ikptr
-ik_mmap_typed(int size, unsigned int type, ikpcb* pcb){
+ik_mmap_typed(long int size, unsigned int type, ikpcb* pcb){
   ikptr p;
   if(size == pagesize) {
     ikpage* s = pcb->cached_pages;
@@ -181,17 +181,17 @@ ik_mmap_typed(int size, unsigned int type, ikpcb* pcb){
 }
 
 ikptr
-ik_mmap_ptr(int size, int gen, ikpcb* pcb){
+ik_mmap_ptr(long int size, int gen, ikpcb* pcb){
   return ik_mmap_typed(size, pointers_mt | gen, pcb);
 }
 
 ikptr
-ik_mmap_data(int size, int gen, ikpcb* pcb){
+ik_mmap_data(long int size, int gen, ikpcb* pcb){
   return ik_mmap_typed(size, data_mt | gen, pcb);
 }
 
 ikptr
-ik_mmap_code(int size, int gen, ikpcb* pcb){
+ik_mmap_code(long int size, int gen, ikpcb* pcb){
   ikptr p = ik_mmap_typed(size, code_mt | gen, pcb);
   if(size > pagesize){
     set_segment_type(p+pagesize, size-pagesize, data_mt|gen, pcb);
@@ -208,7 +208,7 @@ ik_mmap_code(int size, int gen, ikpcb* pcb){
 
 
 ikptr
-ik_mmap_mixed(int size, ikpcb* pcb){
+ik_mmap_mixed(long int size, ikpcb* pcb){
   return ik_mmap_typed(size, mainheap_mt, pcb);
 }
 
@@ -216,7 +216,7 @@ ik_mmap_mixed(int size, ikpcb* pcb){
 
 
 ikptr
-ik_mmap(int size){
+ik_mmap(long int size){
   int pages = (size + pagesize - 1) / pagesize;
   total_allocated_pages += pages;
   int mapsize = pages * pagesize;
@@ -231,7 +231,7 @@ ik_mmap(int size){
       0);
   /* FIXME: check if in range */
   if(mem == MAP_FAILED){
-    fprintf(stderr, "Mapping failed: %s\n", strerror(errno));
+    fprintf(stderr, "Mapping (0x%lx bytes) failed: %s\n", size, strerror(errno));
     exit(-1);
   }
 #else
@@ -246,7 +246,7 @@ ik_mmap(int size){
 }
 
 void
-ik_munmap(ikptr mem, int size){
+ik_munmap(ikptr mem, long int size){
   int pages = (size + pagesize - 1) / pagesize;
   int mapsize = pages * pagesize;
   assert(size == mapsize);