Index: runtime/src/kmp.h
===================================================================
--- runtime/src/kmp.h
+++ runtime/src/kmp.h
@@ -596,7 +596,11 @@
 extern size_t __kmp_affin_mask_size;
 #define KMP_AFFINITY_CAPABLE() (__kmp_affin_mask_size > 0)
 #define KMP_AFFINITY_DISABLE() (__kmp_affin_mask_size = 0)
-#define KMP_AFFINITY_ENABLE(mask_size) (__kmp_affin_mask_size = mask_size)
+// Round to the nearest multiple of sizeof(unsigned long), which is the
+// size of mask_t.
+#define KMP_AFFINITY_ENABLE(mask_size) \
+  (__kmp_affin_mask_size = ((mask_size + sizeof(unsigned long) - 1) &          \
+                           ~(sizeof(unsigned long)-1)))
 #define KMP_CPU_SET_ITERATE(i, mask)                                           \
   for (i = (mask)->begin(); (int)i != (mask)->end(); i = (mask)->next(i))
 #define KMP_CPU_SET(i, mask) (mask)->set(i)
Index: runtime/src/kmp_affinity.h
===================================================================
--- runtime/src/kmp_affinity.h
+++ runtime/src/kmp_affinity.h
@@ -237,12 +237,12 @@
 #endif /* KMP_ARCH_* */
 class KMPNativeAffinity : public KMPAffinity {
   class Mask : public KMPAffinity::Mask {
-    typedef unsigned char mask_t;
+    typedef unsigned long mask_t;
     static const int BITS_PER_MASK_T = sizeof(mask_t) * CHAR_BIT;
 
   public:
     mask_t *mask;
-    Mask() { mask = (mask_t *)__kmp_allocate(__kmp_affin_mask_size); }
+    Mask() { mask = (mask_t *)__kmp_allocate(sizeof(mask_t) * __kmp_affin_mask_size); }
     ~Mask() {
       if (mask)
         __kmp_free(mask);
@@ -296,7 +296,7 @@
       KMP_ASSERT2(KMP_AFFINITY_CAPABLE(),
                   "Illegal get affinity operation when not capable");
       int retval =
-          syscall(__NR_sched_getaffinity, 0, __kmp_affin_mask_size, mask);
+          syscall(__NR_sched_getaffinity, 0, sizeof(mask_t) * __kmp_affin_mask_size, mask);
       if (retval >= 0) {
         return 0;
       }
@@ -310,7 +310,7 @@
       KMP_ASSERT2(KMP_AFFINITY_CAPABLE(),
                   "Illegal get affinity operation when not capable");
       int retval =
-          syscall(__NR_sched_setaffinity, 0, __kmp_affin_mask_size, mask);
+          syscall(__NR_sched_setaffinity, 0, sizeof(mask_t) * __kmp_affin_mask_size, mask);
       if (retval >= 0) {
         return 0;
       }