src/superpose_on_core_2.cpp |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/src/superpose_on_core_2.cpp b/src/superpose_on_core_2.cpp
index ae137de..059dfe3 100644
--- a/src/superpose_on_core_2.cpp
+++ b/src/superpose_on_core_2.cpp
@@ -55,6 +55,8 @@ using std::ofstream ;
 #include "multiple_superposition.h"
 #include "3D_manip_functions.h"
 
+#include <unistd.h>
+
 int **core_columns ;
 int *core_columns_2 , NCORE = 0 ;
 int **algn_to_seq_hash ;