diff --git a/vpxenc.c b/vpxenc.c
index 3fc8da1fe..8de73f7b1 100644
--- a/vpxenc.c
+++ b/vpxenc.c
@@ -10,7 +10,7 @@
 
 #include "vpx_config.h"
 
-#if defined(_WIN32) || !CONFIG_OS_SUPPORT
+#if defined(_WIN32) || defined(__OS2__) || !CONFIG_OS_SUPPORT
 #define USE_POSIX_MMAP 0
 #else
 #define USE_POSIX_MMAP 1