diff --git a/Source/WebKit/ChangeLog b/Source/WebKit/ChangeLog
index 61fb45763a5b..ccc6a4f61394 100644
--- a/Source/WebKit/ChangeLog
+++ b/Source/WebKit/ChangeLog
@@ -1,3 +1,21 @@
+2017-10-16  Adrian Perez de Castro  <aperez@igalia.com>
+
+        [WPE] Build failure due to invalid cast of EGLNativeWindowType when targetting 64-bit ARM
+        https://bugs.webkit.org/show_bug.cgi?id=178090
+
+        Reviewed by Michael Catanzaro.
+
+        EGLNativeWindowType can be aliased to a different type depending (at least) on the EGL
+        implementation, its build options, and the libepoxy build options.  Using "static_cast"
+        works when it is a numeric value and the width of the value needs to be optionally
+        extended to 64 bits (e.g. the EGL type is "int" in a 32-bit CPU) but not for pointers,
+        and using "reinterpret_cast" works when the size of a pointer is 64 bits but not in other
+        cases. Therefore it seems reasonable to use a plain C cast expression to solve this
+        particular situation.
+
+        * WebProcess/WebPage/wpe/AcceleratedSurfaceWPE.cpp:
+        (WebKit::AcceleratedSurfaceWPE::window const): Use a good old plain C cast expression.
+
 2017-10-10  Adrian Perez de Castro  <aperez@igalia.com>
 
         [WPE] Remove the possibility of installing the old WebKit2 C API
diff --git a/Source/WebKit/WebProcess/WebPage/wpe/AcceleratedSurfaceWPE.cpp b/Source/WebKit/WebProcess/WebPage/wpe/AcceleratedSurfaceWPE.cpp
index cbe88dd5a873..f0e6521a5f10 100644
--- a/Source/WebKit/WebProcess/WebPage/wpe/AcceleratedSurfaceWPE.cpp
+++ b/Source/WebKit/WebProcess/WebPage/wpe/AcceleratedSurfaceWPE.cpp
@@ -75,7 +75,12 @@ void AcceleratedSurfaceWPE::finalize()
 uint64_t AcceleratedSurfaceWPE::window() const
 {
     ASSERT(m_backend);
-    return reinterpret_cast<uint64_t>(wpe_renderer_backend_egl_target_get_native_window(m_backend));
+    // EGLNativeWindowType changes depending on the EGL implementation: reinterpret_cast works
+    // for pointers (only if they are 64-bit wide and not for other cases), and static_cast for
+    // numeric types (and when needed they get extended to 64-bit) but not for pointers. Using
+    // a plain C cast expression in this one instance works in all cases.
+    static_assert(sizeof(EGLNativeWindowType) <= sizeof(uint64_t), "EGLNativeWindowType must not be longer than 64 bits.");
+    return (uint64_t) wpe_renderer_backend_egl_target_get_native_window(m_backend);
 }
 
 uint64_t AcceleratedSurfaceWPE::surfaceID() const