diff --git a/libc/bionic/libc_init_static.cpp b/libc/bionic/libc_init_static.cpp
index ef57af6..2b1a8cb 100644
--- a/libc/bionic/libc_init_static.cpp
+++ b/libc/bionic/libc_init_static.cpp
@@ -49,16 +49,10 @@
 #include "libc_init_common.h"
 #include "pthread_internal.h"
 
+#include "private/bionic_page.h"
 #include "private/bionic_tls.h"
 #include "private/KernelArgumentBlock.h"
 
-// Returns the address of the page containing address 'x'.
-#define PAGE_START(x)  ((x) & PAGE_MASK)
-
-// Returns the address of the next page after address 'x', unless 'x' is
-// itself at the start of a page.
-#define PAGE_END(x)    PAGE_START((x) + (PAGE_SIZE-1))
-
 extern "C" int __cxa_atexit(void (*)(void *), void *, void *);
 
 static void call_array(void(**list)()) {
diff --git a/libc/include/limits.h b/libc/include/limits.h
index 6ae629b..685e184 100644
--- a/libc/include/limits.h
+++ b/libc/include/limits.h
@@ -89,9 +89,6 @@
 #define  PAGESIZE  PAGE_SIZE
 #endif
 
-/* glibc's PAGE_MASK is the bitwise negation of BSD's! TODO: remove? */
-#define PAGE_MASK (~(PAGE_SIZE - 1))
-
 #define SEM_VALUE_MAX 0x3fffffff
 
 /* POSIX says these belong in <unistd.h> but BSD has some in <limits.h>. */
diff --git a/libc/include/sys/user.h b/libc/include/sys/user.h
index d63fe6a..12af664 100644
--- a/libc/include/sys/user.h
+++ b/libc/include/sys/user.h
@@ -35,6 +35,9 @@
 
 __BEGIN_DECLS
 
+#define PAGE_SIZE 4096
+#define PAGE_MASK (~(PAGE_SIZE - 1))
+
 #if __i386__
 
 struct user_fpregs_struct {
diff --git a/libc/private/bionic_page.h b/libc/private/bionic_page.h
new file mode 100644
index 0000000..0beb708
--- /dev/null
+++ b/libc/private/bionic_page.h
@@ -0,0 +1,33 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _BIONIC_PAGE_H_
+#define _BIONIC_PAGE_H_
+
+// Get PAGE_SIZE and PAGE_MASK.
+#include <sys/user.h>
+
+// Returns the address of the page containing address 'x'.
+#define PAGE_START(x) ((x) & PAGE_MASK)
+
+// Returns the offset of address 'x' in its page.
+#define PAGE_OFFSET(x) ((x) & ~PAGE_MASK)
+
+// Returns the address of the next page after address 'x', unless 'x' is
+// itself at the start of a page.
+#define PAGE_END(x) PAGE_START((x) + (PAGE_SIZE-1))
+
+#endif // _BIONIC_PAGE_H_