diff --git a/build.xml b/build.xml
index 49e2046..6d64d40 100644
--- a/build.xml
+++ b/build.xml
@@ -48,25 +48,25 @@
 <java classname="micropolisj.build_tool.MakeTiles" classpath="${builddir}"
 	fork="true" failonerror="true" dir="graphics" inputstring="">
 	<arg file="graphics/tiles.rc" />
-	<arg file="${builddir}/tiles.png" />
+	<arg file="${builddir}/16x16" />
 </java>
 <java classname="micropolisj.build_tool.MakeTiles" classpath="${builddir}"
 	fork="true" failonerror="true" dir="graphics" inputstring="">
 	<sysproperty key="tile_size" value="8" />
 	<arg file="graphics/tiles.rc" />
-	<arg file="${builddir}/tiles_8x8.png" />
+	<arg file="${builddir}/8x8" />
 </java>
 <java classname="micropolisj.build_tool.MakeTiles" classpath="${builddir}"
 	fork="true" failonerror="true" dir="graphics" inputstring="">
 	<sysproperty key="tile_size" value="32" />
 	<arg file="graphics/tiles.rc" />
-	<arg file="${builddir}/tiles_32x32.png" />
+	<arg file="${builddir}/32x32" />
 </java>
 <java classname="micropolisj.build_tool.MakeTiles" classpath="${builddir}"
 	fork="true" failonerror="true" dir="graphics" inputstring="">
 	<sysproperty key="tile_size" value="3" />
 	<arg file="graphics/tiles.rc" />
-	<arg file="${builddir}/tilessm.png" />
+	<arg file="${builddir}/sm" />
 </java>
 <copy todir="${builddir}" file="graphics/tiles.rc" />
 </target>
diff --git a/src/micropolisj/build_tool/MakeTiles.java b/src/micropolisj/build_tool/MakeTiles.java
index e79f91e..9ddc483 100644
--- a/src/micropolisj/build_tool/MakeTiles.java
+++ b/src/micropolisj/build_tool/MakeTiles.java
@@ -39,12 +39,12 @@ public class MakeTiles
 		}
 
 		File recipeFile = new File(args[0]);
-		File outputFile = new File(args[1]);
+		File outputDir = new File(args[1]);
 
-		generateFromRecipe(recipeFile, outputFile);
+		generateFromRecipe(recipeFile, outputDir);
 	}
 
-	static void generateFromRecipe(File recipeFile, File outputFile)
+	static void generateFromRecipe(File recipeFile, File outputDir)
 		throws IOException
 	{
 		Properties recipe = new Properties();
@@ -82,15 +82,17 @@ public class MakeTiles
 			drawTo(ref, gr, 0, TILE_SIZE*i);
 		}
 
+		// make parent directories if necessary
+		outputDir.mkdirs();
+
+		// output the composed images
+		File outputFile = new File(outputDir, "tiles.png");
 		System.out.println("Generating tiles array: "+outputFile);
 		ImageIO.write(buf, "png", outputFile);
 
-		File indexFile = new File(
-				outputFile.getParentFile(),
-				outputFile.getName()
-					.replaceFirst("\\.png$","")
-					+ ".idx"
-				);
+		// output an index of all tile names and their offset into
+		// the composed tile array
+		File indexFile = new File(outputDir, "tiles.idx");
 		System.out.println("Generating tiles index: "+indexFile);
 		writeIndexFile(tileNames, indexFile);
 	}