diff --git a/src/fontgen/fontgen.c b/src/fontgen/fontgen.c
index f97cff0..d2d418e 100644
--- a/src/fontgen/fontgen.c
+++ b/src/fontgen/fontgen.c
@@ -192,24 +192,24 @@ int main(int argc, char * argv[])
     {
         if ((char_infos[i].width < 0) || (char_infos[i].width > max_advance))
         {
-            fprintf(stderr, "Error: invalid character %d width: %d\n", i, char_infos[i].width);
+            fprintf(stderr, "Error: invalid character %d width: %d (max advance %d)\n", i, char_infos[i].width, max_advance);
             return false;
         }
         if ((char_infos[i].height < 0) || (char_infos[i].height > line_height))
         {
-            fprintf(stderr, "Error: invalid character %d height: %d\n", i, char_infos[i].height);
+            fprintf(stderr, "Error: invalid character %d height: %d (line height %d)\n", i, char_infos[i].height, line_height);
             return false;
         }
         if ((char_infos[i].left < 0) || (char_infos[i].left >= max_advance))
         {
-            fprintf(stderr, "Error: invalid character %d left: %d\n", i, char_infos[i].left);
+            fprintf(stderr, "Error: invalid character %d left: %d (max advance %d)\n", i, char_infos[i].left, max_advance);
             return false;
         }
         /* Adjust character top to be index downward from top of font box. */
         char_infos[i].top = line_height - baseline_offset - char_infos[i].top;
         if ((char_infos[i].top < 0) || (char_infos[i].top >= line_height))
         {
-            fprintf(stderr, "Error: invalid character %d top: %d\n", i, char_infos[i].top);
+            fprintf(stderr, "Error: invalid character %d top: %d (line height %d)\n", i, char_infos[i].top, line_height);
             return false;
         }
         if ((char_infos[i].left + char_infos[i].width) > max_advance)