diff --git a/bin/mrdna b/bin/mrdna
index bf470589ee50754ee1cebcbba7789b4f8fe503bb..0c7d04e4d7bcd0194f4f9acde14f0f825d63a4ed 100755
--- a/bin/mrdna
+++ b/bin/mrdna
@@ -113,7 +113,7 @@ def main():
     model = read_model( str(infile), debye_length=args.debye_length, temperature=args.temperature )
 
     if args.dimensions is None:
-        dim = model.dimensions_from_structure( padding_factor=2.5 )
+        dim = [max(x,1000) for x in model.dimensions_from_structure( padding_factor=2.5 )]
         model.dimensions = dim
         model.origin = model.get_center()-0.5*np.array(model.dimensions)
     else: