diff --git a/changelog.md b/changelog.md
index e0fd649428..87bf8bd08e 100644
--- a/changelog.md
+++ b/changelog.md
@@ -126,6 +126,7 @@
 
 ### Tool changes
 
+- Fix Nimpretty must not accept negative indentation argument because breaks file.
 
 
 ### Compiler changes
diff --git a/nimpretty/nimpretty.nim b/nimpretty/nimpretty.nim
index 95f4285984..50d0d725f8 100644
--- a/nimpretty/nimpretty.nim
+++ b/nimpretty/nimpretty.nim
@@ -44,8 +44,8 @@ proc writeVersion() =
 
 type
   PrettyOptions = object
-    indWidth: int
-    maxLineLen: int
+    indWidth: Natural
+    maxLineLen: Positive
 
 proc prettyPrint(infile, outfile: string, opt: PrettyOptions) =
   var conf = newConfigRef()