diff --git a/include/Makefile.am b/include/Makefile.am
index b1be9f9..74f6fe7 100644
--- a/include/Makefile.am
+++ b/include/Makefile.am
@@ -6,6 +6,7 @@ noinst_HEADERS += sys/queue.h
 noinst_HEADERS += sys/socket.h
 noinst_HEADERS += sys/types.h
 noinst_HEADERS += sys/time.h
+noinst_HEADERS += sys/mman.h
 noinst_HEADERS += err.h
 noinst_HEADERS += ifaddrs.h
 noinst_HEADERS += imsg.h
diff --git a/include/sys/mman.h b/include/sys/mman.h
new file mode 100644
index 0000000..d9eb6a9
--- /dev/null
+++ b/include/sys/mman.h
@@ -0,0 +1,19 @@
+/*
+ * Public domain
+ * sys/mman.h compatibility shim
+ */
+
+#include_next <sys/mman.h>
+
+#ifndef LIBCRYPTOCOMPAT_MMAN_H
+#define LIBCRYPTOCOMPAT_MMAN_H
+
+#ifndef MAP_ANON
+#ifdef MAP_ANONYMOUS
+#define MAP_ANON MAP_ANONYMOUS
+#else
+#error "System does not support mapping anonymous pages?"
+#endif
+#endif
+
+#endif