use '-' instead of '_' for lmc options.
diff --git a/build_images.py b/build_images.py
index 48b0cba..f176939 100755
--- a/build_images.py
+++ b/build_images.py
@@ -183,7 +183,7 @@
     size = BINARIES[binary]
 
     args = [lmc,
-                '--image_size', size,
+                '--image-size', size,
                 '--hwpack-force-yes',
                 '--hwpack', hwpack_file,
                 '--binary', binary_file,
@@ -192,10 +192,10 @@
     if fastmodel:
         args += ['--dev', 'fastmodel',
                 '--output-directory', os.path.dirname(imgfile),
-                '--image_file', os.path.basename(imgfile)]
+                '--image-file', os.path.basename(imgfile)]
     else:
         args += ['--dev', hwpi.lmcname,
-                '--image_file', imgfile]
+                '--image-file', imgfile]
 
     if hwpi.pre_inst_script is not None:
         sdir = os.path.abspath(os.path.dirname(__file__))