--- a/src/output.cpp
+++ b/src/output.cpp
@@ -163,7 +163,7 @@
   m_pFile->Write(acBuf, strlen(acBuf));
   sprintf(acBuf, "%s", "# generated with SffToBmp\n");
   m_pFile->Write(acBuf, strlen(acBuf));
-  sprintf(acBuf, "%ld %ld\n", aWidth, aHeight);
+  sprintf(acBuf, "%u %u\n", aWidth, aHeight);
   m_pFile->Write(acBuf, strlen(acBuf));
 }