--- a/tools/gfxconv.c	Mon Feb 23 22:51:28 2015 +0200
+++ b/tools/gfxconv.c	Mon Feb 23 22:51:51 2015 +0200
@@ -1247,6 +1247,7 @@
 
 int dmWriteSpritesAndChars(const char *filename, DMImage *image, int outFormat, BOOL multicolor)
 {
+    int ret = DMERR_OK;
     int outBlockW, outBlockH, bx, by;
     FILE *outFile = NULL;
     Uint8 *buf = NULL;
@@ -1270,12 +1271,14 @@
             break;
 
         default:
+            ret = DMERR_INVALID_ARGS;
             dmError("Invalid output format %d, internal error.\n", outFormat);
             goto error;
     }
 
-    if (outBlockW <= 0 || outBlockH <= 0)
+    if (outBlockW < 1 || outBlockH < 1)
     {
+        ret = DMERR_INVALID_ARGS;
         dmError("Source image dimensions too small for conversion, block dimensions %d x %d.\n",
             outBlockW, outBlockH);
         goto error;
@@ -1283,9 +1286,9 @@
 
     if ((outFile = fopen(filename, "wb")) == NULL)
     {
-        int err = dmGetErrno();
+        ret = dmGetErrno();
         dmError("Could not open '%s' for writing, %d: %s.\n",
-            filename, err, dmErrorStr(err));
+            filename, ret, dmErrorStr(ret));
         goto error;
     }
 
@@ -1308,21 +1311,27 @@
                 if (!dmConvertImage2Char(buf, image,
                     bx * C64_CHR_WIDTH_PX, by * C64_CHR_HEIGHT,
                     multicolor))
+                {
+                    ret = DMERR_DATA_ERROR;
                     goto error;
+                }
                 break;
 
             case FFMT_SPRITE:
                 if (!dmConvertImage2Sprite(buf, image,
                     bx * C64_SPR_WIDTH_PX, by * C64_SPR_HEIGHT,
                     multicolor))
+                {
+                    ret = DMERR_DATA_ERROR;
                     goto error;
+                }
         }
 
         if (!dm_fwrite_str(outFile, buf, outBufSize))
         {
-            int err = dmGetErrno();
+            ret = dmGetErrno();
             dmError("Error writing data block %d,%d to '%s', %d: %s\n",
-                bx, by, filename, err, dmErrorStr(err));
+                bx, by, filename, ret, dmErrorStr(ret));
             goto error;
         }
     }