diff --git a/Misc/NEWS b/Misc/NEWS
index 3325966..25a51a6 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -14,8 +14,8 @@
   format string that contains positional fields. Initial patch by
   Julian Berman.
 
-- Issue #11627: Fix segfault when __new__ on a exception returns a non-exception
-  class.
+- Issue #11627: Fix segfault when __new__ on a exception returns a
+  non-exception class.
 
 - Issue #12149: Update the method cache after a type's dictionnary gets
   cleared by the garbage collector.  This fixes a segfault when an instance
@@ -71,6 +71,13 @@
 - Issue #12451: xml.dom.pulldom: parse() now opens files in binary mode instead
   of the text mode (using the locale encoding) to avoid encoding issues.
 
+Extension Modules
+-----------------
+
+- Issue #10309: Define _GNU_SOURCE so that mremap() gets the proper
+  signature.  Without this, architectures where sizeof void* != sizeof int are
+  broken.  Patch given by Hallvard B Furuseth.
+
 C-API
 -----
 
diff --git a/Modules/_ctypes/libffi/src/dlmalloc.c b/Modules/_ctypes/libffi/src/dlmalloc.c
index 783c5c2..582ddc3 100644
--- a/Modules/_ctypes/libffi/src/dlmalloc.c
+++ b/Modules/_ctypes/libffi/src/dlmalloc.c
@@ -457,6 +457,11 @@
 #define LACKS_ERRNO_H
 #define MALLOC_FAILURE_ACTION
 #define MMAP_CLEARS 0 /* WINCE and some others apparently don't clear */
+#elif !defined _GNU_SOURCE
+/* mremap() on Linux requires this via sys/mman.h
+ * See roundup issue 10309
+ */
+#define _GNU_SOURCE 1
 #endif  /* WIN32 */
 
 #if defined(DARWIN) || defined(_DARWIN)