diff --git a/Makefile.am b/Makefile.am
index 5c9e7882b8..7388a4ef50 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -48,8 +48,10 @@ rpmdist: dist
 doxydoc:
 	cd sourcedoc; $(MAKE) doxydoc
 
-lfundoc:
-	development/tools/gen_lfuns.py src/LyXAction.cpp > lib/doc/LFUNs.lyx
+lfundoc: $(srcdir)/lib/doc/LFUNs.lyx
+
+$(srcdir)/lib/doc/LFUNs.lyx: $(srcdir)/development/tools/gen_lfuns.py $(srcdir)/src/LyXAction.cpp
+	$(AM_V_GEN)$(PYTHON) $^ >$@ 2>/dev/null
 
 keystest:
 	development/keystest/lyx_make.sh
diff --git a/development/tools/gen_lfuns.py b/development/tools/gen_lfuns.py
index acb2c17818..e8a91062dd 100755
--- a/development/tools/gen_lfuns.py
+++ b/development/tools/gen_lfuns.py
@@ -377,14 +377,14 @@ def write_sections(file,lfuns):
                 write_fields(file, lf)
     
 def main(argv):
-    # parse command line arguments   
+    # parse command line arguments
     script_path, script_name = os.path.split(argv[0])
     if len(argv) < 2:
         error(usage(script_name))
     # input file
     lyxaction_path = argv[1]
-    if not os.path.exists(lyxaction_path):
-        error(script_name + ": %s is not a valid path" % lyxaction_path, usage(argv[0]))
+    if not os.path.isfile(lyxaction_path):
+        error(script_name + ": %s is not a valid path" % lyxaction_path)
 
     # output file
     if len(argv) == 3: