diff --git a/src/_ct_shared.h b/src/_ct_shared.h
deleted file mode 100644
index ace046c..0000000
--- a/src/_ct_shared.h
+++ /dev/null
@@ -1,15 +0,0 @@
-#ifndef _CURSETREE__SHARED_H
-#define _CURSETREE__SHARED_H
-
-/* Standard success/failure status codes. */
-#define OK (0)
-#define ERR (1)
-
-/* Initial row and column coordinates. */
-#define ROW0 1
-#define COL0 1
-
-typedef unsigned short pos;
-typedef unsigned char glyph;
-
-#endif /* _CURSETREE__SHARED_H */
diff --git a/src/ct_shared.h b/src/ct_shared.h
new file mode 100644
index 0000000..cbcd936
--- /dev/null
+++ b/src/ct_shared.h
@@ -0,0 +1,19 @@
+#ifndef CURSETREE_SHARED_H
+#define CURSETREE_SHARED_H
+
+/* Standard success/failure status codes.
+ * NERR is used when positive integers are reserved
+ * for non-error value return codes on success.
+ */
+#define OK (0)
+#define ERR (1)
+#define NERR (-1)
+
+/* Initial row and column coordinates. */
+#define ROW0 1
+#define COL0 1
+
+typedef unsigned short pos;
+typedef unsigned char glyph;
+
+#endif /* CURSETREE_SHARED_H */
diff --git a/src/surface.c b/src/surface.c
index 78c9935..883f3e4 100644
--- a/src/surface.c
+++ b/src/surface.c
@@ -1,7 +1,7 @@
 #include <errno.h>
 #include <stdlib.h>
 
-#include "_ct_shared.h"
+#include "ct_shared.h"
 #include "surface.h"
 
 #define ALLOC_COLS(w) ((glyph *)calloc(w, sizeof(glyph)))
diff --git a/src/surface.h b/src/surface.h
index 6697e15..d563e54 100644
--- a/src/surface.h
+++ b/src/surface.h
@@ -1,7 +1,7 @@
 #ifndef _CURSETREE_SURFACE_H
 #define _CURSETREE_SURFACE_H
 
-#include "_ct_shared.h"
+#include "ct_shared.h"
 
 typedef struct ct_surface {
   pos x, y, w, h;