diff --git a/dev/tests/filesystem.lua b/dev/tests/filesystem.lua
index 38e7c4a04..80c080cdd 100644
--- a/dev/tests/filesystem.lua
+++ b/dev/tests/filesystem.lua
@@ -1,3 +1,8 @@
+debug.log("file extension")
+asserts.equals(nil, file.ext("config:test"))
+asserts.equals("cfg", file.ext("config:test.cfg"))
+asserts.equals("gz", file.ext("config:test.cfg.gz"))
+
 debug.log("check initial state")
 assert(file.exists("config:"))
 
diff --git a/res/modules/internal/extensions/file.lua b/res/modules/internal/extensions/file.lua
index d308eda9c..b19864cf6 100644
--- a/res/modules/internal/extensions/file.lua
+++ b/res/modules/internal/extensions/file.lua
@@ -8,7 +8,7 @@ function file.stem(path)
 end
 
 function file.ext(path)
-    return path:match("%.([^:/\\]+)$")
+    return path:match("[^:/\\.]%.([^.:/\\]+)$")
 end
 
 function file.prefix(path)