diff --git a/ueforth/common/core.h b/ueforth/common/core.h
index d51cf05..f5f9aa4 100644
--- a/ueforth/common/core.h
+++ b/ueforth/common/core.h
@@ -13,7 +13,9 @@ static struct {
 static cell_t convert(const char *pos, cell_t n, cell_t *ret) {
   *ret = 0;
   cell_t negate = 0;
+  cell_t base = g_sys.base;
   if (!n) { return 0; }
+  if (pos[0] == '$') { base = 16; ++pos; --n; }
   if (pos[0] == '-') { negate = -1; ++pos; --n; }
   for (; n; --n) {
     uintptr_t d = pos[0] - '0';
@@ -22,7 +24,7 @@ static cell_t convert(const char *pos, cell_t n, cell_t *ret) {
       if (d < 10) { return 0; }
     }
     if (d >= (uintptr_t) g_sys.base) { return 0; }
-    *ret = *ret * g_sys.base + d;
+    *ret = *ret * base + d;
     ++pos;
   }
   if (negate) { *ret = -*ret; }
diff --git a/ueforth/posix/posix.fs b/ueforth/posix/posix.fs
index 2860d44..9b2efbf 100644
--- a/ueforth/posix/posix.fs
+++ b/ueforth/posix/posix.fs
@@ -38,6 +38,14 @@ z" __errno_location" 0 sysfunc __errno_location
 1 constant SEEK_CUR
 2 constant SEEK_END
 
+( mmap )
+0 constant PROT_NONE
+1 constant PROT_READ
+2 constant PROT_WRITE
+4 constant PROT_EXEC
+$10 constant MAP_FIXED
+$20 constant MAP_ANONYMOUS
+
 ( Terminal handling )
 : n. ( n -- ) base @ swap decimal <# #s #> type base ! ;
 : esc   27 emit ;