diff --git a/Makefile b/Makefile
index 6bc97fd..d9536a1 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
-BITMAPS:=$(patsubst parts/%.dat, bitmaps/%.png, $(wildcard parts/*.dat))
-BITMAPSWF:=$(patsubst parts/%.dat, bitmaps-wireframe/%.png, $(wildcard parts/*.dat))
+BITMAPS:=$(patsubst parts/%.dat, bitmaps/%.png, $(wildcard parts/[0-9]*.dat))
+BITMAPSWF:=$(patsubst parts/%.dat, bitmaps-wireframe/%.png, $(wildcard parts/[0-9]*.dat))
 NORMALIZED:=$(patsubst parts/%.dat, normalized/%.dat, $(wildcard parts/*.dat))
 
 all: parts