diff --git a/generators/image.h b/generators/image.h
index 2013f2f..3a50da0 100644
--- a/generators/image.h
+++ b/generators/image.h
@@ -11,7 +11,7 @@ pixel[1] = header_data_cmap[(unsigned char)data[0]][1]; \
 pixel[2] = header_data_cmap[(unsigned char)data[0]][2]; \
 data ++; }
 
-static char header_data_cmap[256][3] = {
+static unsigned char header_data_cmap[256][3] = {
 	{  0,  0,  0},
 	{255,255,255},
 	{255,255,255},