--- a/js/src/vm/Stack.cpp
+++ b/js/src/vm/Stack.cpp
@@ -822,22 +822,21 @@ StackSpace::sizeOf()
      * which are swapped out to disk.  We really should, but what we have here
      * is better than counting the whole stack!
      */
 
     const int pageSize = getpagesize();
     size_t numBytes = (trustedEnd_ - base_) * sizeof(Value);
     size_t numPages = (numBytes + pageSize - 1) / pageSize;
 
-    // On Linux, mincore's third argument has type unsigned char*.  On Mac, it
-    // has type char*.
-#if defined(XP_MACOSX)
+    // On Linux, mincore's third argument has type unsigned char*.
+#ifdef __linux__
+    typedef unsigned char MincoreArgType;
+#else
     typedef char MincoreArgType;
-#else
-    typedef unsigned char MincoreArgType;
 #endif
 
     MincoreArgType *vec = (MincoreArgType *) js_malloc(numPages);
     int result = mincore(base_, numBytes, vec);
     if (result) {
         js_free(vec);
         /*
          * If mincore fails us, return the vsize (like we do below if we're not