diff --git a/doomsday/cmake/merge_sources.py b/doomsday/cmake/merge_sources.py
index 189413997e..0bb4398918 100755
--- a/doomsday/cmake/merge_sources.py
+++ b/doomsday/cmake/merge_sources.py
@@ -8,7 +8,7 @@
 code = []
 
 # Read and process all input source files.
-for fn in sys.argv[2:]:
+for fn in sorted(sys.argv[2:]):
     preamble = True
     in_body = False
     if_level = 0