diff -r 5f4402180204 -r e3974e7360e9 src/Platform-Posix.cpp
--- a/src/Platform-Posix.cpp	Wed Jul 25 00:48:08 2012 -0700
+++ b/src/Platform-Posix.cpp	Wed Jul 25 01:30:33 2012 -0700
@@ -72,7 +72,7 @@
     }
 
     size_t requested = Min(amount * 2, amount + 2 * alignment);
-    Address address = MapMemory(amount, mode, Prot_ReadWrite);
+    Address address = MapMemory(requested, mode, Prot_ReadWrite);
     if (!address)
         return AlignableMapping();
 
@@ -87,7 +87,7 @@
 
     if (requested - begin > amount) {
         // Shave off the last part of the unaligned region.
-        UnmapAlignedMemory(address + amount, requested - amount - begin);
+        UnmapAlignedMemory(aligned + amount, requested - amount - begin);
     }
 
     return AlignableMapping(aligned, alignment, amount);