diff --git a/src/kern/operatingsystem.hh b/src/kern/operatingsystem.hh
index 47e64ffd9..6574e3c6b 100644
--- a/src/kern/operatingsystem.hh
+++ b/src/kern/operatingsystem.hh
@@ -122,6 +122,10 @@ class OperatingSystem {
 
     static int openSpecialFile(std::string path, LiveProcess *process, ThreadContext *tc);
 
+    static const bool mmapGrowsUp = true;
+
+    static bool mmapGrowsDown() { return false; }
+
 };  // class OperatingSystem
 
 
diff --git a/src/sim/syscall_emul.hh b/src/sim/syscall_emul.hh
index c9ce4b14f..e45a6c797 100644
--- a/src/sim/syscall_emul.hh
+++ b/src/sim/syscall_emul.hh
@@ -978,9 +978,14 @@ mmapFunc(SyscallDesc *desc, int num, LiveProcess *p, ThreadContext *tc)
     }
 
     // pick next address from our "mmap region"
-    start = p->mmap_end;
+    if (OS::mmapGrowsDown()) {
+        start = p->mmap_end - length;
+        p->mmap_end = start;
+    } else {
+        start = p->mmap_end;
+        p->mmap_end += length;
+    }
     p->pTable->allocate(start, length);
-    p->mmap_end += length;
 
     if (!(flags & OS::TGT_MAP_ANONYMOUS)) {
         warn("allowing mmap of file @ fd %d. "