diff --git a/src/scim_hangul_imengine.cpp b/src/scim_hangul_imengine.cpp
index 7d70654..d678902 100644
--- a/src/scim_hangul_imengine.cpp
+++ b/src/scim_hangul_imengine.cpp
@@ -30,6 +30,7 @@
 #define Uses_SCIM_CONFIG_BASE
 
 #include <cstring>
+#include <unistd.h>
 #ifdef HAVE_CONFIG_H
   #include <config.h>
 #endif