diff --git a/src/fontgen/fontgen.c b/src/fontgen/fontgen.c
index 9447612..f97cff0 100644
--- a/src/fontgen/fontgen.c
+++ b/src/fontgen/fontgen.c
@@ -1,5 +1,6 @@
 #include <stdlib.h>
 #include <stdint.h>
+#include <stdbool.h>
 #include <ft2build.h>
 #include <stdio.h>
 #include FT_FREETYPE_H
@@ -86,36 +87,43 @@ static void generate_bytes(FILE * file, const uint8_t * bytes, int count)
     }
 }
 
-static void generate(const char * d_file_name)
+static bool generate(const char * d_file_name)
 {
     FILE * fh = fopen(d_file_name, "wb");
     fprintf(fh, "module hulk.kfont;\n");
     fprintf(fh, "struct CharInfo {\n");
-    fprintf(fh, "    uint width;\n");
-    fprintf(fh, "    uint height;\n");
-    fprintf(fh, "    int top;\n");
-    fprintf(fh, "    int left;\n");
+    fprintf(fh, "    /** Glyph bitmap width. */\n");
+    fprintf(fh, "    ubyte width;\n");
+    fprintf(fh, "    /** Glyph bitmap height. */\n");
+    fprintf(fh, "    ubyte height;\n");
+    fprintf(fh, "    /** Glyph bitmap top offset (descent from top of text row). */\n");
+    fprintf(fh, "    ubyte top;\n");
+    fprintf(fh, "    /** Glyph bitmap left offset. */\n");
+    fprintf(fh, "    ubyte left;\n");
+    fprintf(fh, "    /** Glyph bitmap. */\n");
     fprintf(fh, "    const ubyte[] bitmap;\n");
     fprintf(fh, "};\n");
     fprintf(fh, "struct FontInfo {\n");
-    fprintf(fh, "    uint line_height;\n");
-    fprintf(fh, "    uint advance;\n");
-    fprintf(fh, "    int baseline_offset;\n");
+    fprintf(fh, "    /** Font line height. */\n");
+    fprintf(fh, "    ubyte line_height;\n");
+    fprintf(fh, "    /** Font advance. */\n");
+    fprintf(fh, "    ubyte advance;\n");
+    fprintf(fh, "    /** Characters. */\n");
     fprintf(fh, "    const CharInfo[] chars;\n");
     fprintf(fh, "};\n");
+    fprintf(fh, "/** Kernel font data. */\n");
     fprintf(fh, "__gshared const FontInfo Kfont = {\n");
     fprintf(fh, "    %du,\n", line_height);
     fprintf(fh, "    %du,\n", max_advance);
-    fprintf(fh, "    %d,\n", baseline_offset);
     fprintf(fh, "    [\n");
     for (int i = 0; i < N_CHARS; i++)
     {
         fprintf(fh, "        /* %d */", i);
         fprintf(fh, "        CharInfo(\n");
-        fprintf(fh, "            %du,\n", char_infos[i].width);
-        fprintf(fh, "            %du,\n", char_infos[i].height);
-        fprintf(fh, "            %d,\n", char_infos[i].top);
-        fprintf(fh, "            %d,\n", char_infos[i].left);
+        fprintf(fh, "            %du /* width */,\n", char_infos[i].width);
+        fprintf(fh, "            %du /* height */,\n", char_infos[i].height);
+        fprintf(fh, "            %du /* top */,\n", char_infos[i].top);
+        fprintf(fh, "            %du /* left */,\n", char_infos[i].left);
         if (char_infos[i].width > 0)
         {
             fprintf(fh, "            [\n");
@@ -131,6 +139,7 @@ static void generate(const char * d_file_name)
     fprintf(fh, "    ],\n");
     fprintf(fh, "};\n");
     fclose(fh);
+    return true;
 }
 
 int main(int argc, char * argv[])
@@ -168,7 +177,59 @@ int main(int argc, char * argv[])
     line_height = round_up_26_6(face->size->metrics.height);
     baseline_offset = (line_height - (max_top - min_bottom)) / 2 - min_bottom;
 
-    generate(out_file);
+    if ((line_height < 1) || (line_height > 0xFF))
+    {
+        fprintf(stderr, "Error: invalid line_height %d\n", line_height);
+        return false;
+    }
+    if ((max_advance < 1) || (max_advance > 0xFF))
+    {
+        fprintf(stderr, "Error: invalid max_advance %d\n", max_advance);
+        return false;
+    }
+
+    for (int i = 0; i < N_CHARS; i++)
+    {
+        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);
+            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);
+            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);
+            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);
+            return false;
+        }
+        if ((char_infos[i].left + char_infos[i].width) > max_advance)
+        {
+            fprintf(stderr, "Error: character %d left (%d) + width (%d) > advance (%d)\n",
+                    i, char_infos[i].left, char_infos[i].width, max_advance);
+            return false;
+        }
+        if ((char_infos[i].top + char_infos[i].height) > line_height)
+        {
+            fprintf(stderr, "Error: character %d top (%d) + height (%d) > line height (%d)\n",
+                    i, char_infos[i].top, char_infos[i].height, line_height);
+            return false;
+        }
+    }
+
+    if (!generate(out_file))
+    {
+        return 1;
+    }
 
     return 0;
 }
diff --git a/src/hulk/console.d b/src/hulk/console.d
index a6205b5..dc48e9d 100644
--- a/src/hulk/console.d
+++ b/src/hulk/console.d
@@ -86,7 +86,7 @@ struct Console
     private static void render_char(size_t x, size_t y, char ch)
     {
         const(CharInfo) * ci = &Kfont.chars[ch];
-        Fb.blit_alpha_bitmap(fb_x(x) + ci.left, fb_y(y) + Kfont.line_height - Kfont.baseline_offset - ci.top, ci.bitmap, ci.width, ci.height);
+        Fb.blit_alpha_bitmap(fb_x(x) + ci.left, fb_y(y) + ci.top, ci.bitmap, ci.width, ci.height);
     }
 
     /**