thodg/libgit2

diff --git a/include/git2/common.h b/include/git2/common.h
index 57ab9c1..7d3518f 100644
--- a/include/git2/common.h
+++ b/include/git2/common.h
@@ -161,6 +161,9 @@
 /** This feature has not been implemented yet */
 #define GIT_ENOTIMPLEMENTED (GIT_ERROR - 22)
 
+/** A refernce or object of the same name already exists */
+#define GIT_EEXISTS (GIT_ERROR - 23)
+
 GIT_BEGIN_DECL
 
 typedef struct {
diff --git a/src/errors.c b/src/errors.c
index f6b9648..3c0e8eb 100644
--- a/src/errors.c
+++ b/src/errors.c
@@ -28,7 +28,8 @@ static struct {
 	{GIT_EINVALIDPATH, "The path is invalid" },
 	{GIT_EREVWALKOVER, "The revision walker is empty; there are no more commits left to iterate"},
 	{GIT_EINVALIDREFSTATE, "The state of the reference is not valid"},
-	{GIT_ENOTIMPLEMENTED, "This feature has not been implemented yet"}
+	{GIT_ENOTIMPLEMENTED, "This feature has not been implemented yet"},
+	{GIT_EEXISTS, "A reference with this name already exists"}
 };
 
 const char *git_strerror(int num)