diff -up webkitgtk-2.8.0/Source/bmalloc/bmalloc/Algorithm.h.s390_fixes webkitgtk-2.8.0/Source/bmalloc/bmalloc/Algorithm.h
--- webkitgtk-2.8.0/Source/bmalloc/bmalloc/Algorithm.h.s390_fixes	2015-03-04 15:25:17.000000000 +0100
+++ webkitgtk-2.8.0/Source/bmalloc/bmalloc/Algorithm.h	2015-03-27 10:59:40.245010499 +0100
@@ -66,7 +66,7 @@ inline constexpr bool isPowerOfTwo(size_
 template<typename T> inline T roundUpToMultipleOf(size_t divisor, T x)
 {
     BASSERT(isPowerOfTwo(divisor));
-    return reinterpret_cast<T>((reinterpret_cast<uintptr_t>(x) + (divisor - 1)) & ~(divisor - 1));
+    return reinterpret_cast<T>((reinterpret_cast<size_t>(x) + (divisor - 1)) & ~(divisor - 1));
 }
 
 template<size_t divisor, typename T> inline constexpr T roundUpToMultipleOf(T x)
diff -up webkitgtk-2.8.0/Source/bmalloc/bmalloc/Sizes.h.s390_fixes webkitgtk-2.8.0/Source/bmalloc/bmalloc/Sizes.h
--- webkitgtk-2.8.0/Source/bmalloc/bmalloc/Sizes.h.s390_fixes	2015-03-04 15:25:17.000000000 +0100
+++ webkitgtk-2.8.0/Source/bmalloc/bmalloc/Sizes.h	2015-03-27 10:59:40.245010499 +0100
@@ -99,7 +99,7 @@ namespace Sizes {
     inline size_t sizeClass(size_t size)
     {
         static const size_t sizeClassMask = (mediumMax / alignment) - 1;
-        return mask((size - 1) / alignment, sizeClassMask);
+        return mask(static_cast<uintptr_t>((size - 1) / alignment), sizeClassMask);
     }
 
     inline size_t objectSize(size_t sizeClass)