fixes #4220

tests/misc/tunsignedcmp.nim

@@ -1,7 +1,15 @@
 discard """
   output: '''true
 true
-true'''
+true
+5
+4
+3
+2
+1
+0
+it should stop now
+'''
 """
 
 # bug 1420
@@ -11,3 +19,15 @@ echo x > y # works
 
 echo((40'i32) > (30'i32))
 echo((40'u32) > (30'u32)) # Error: ordinal type expected
+
+# bug #4220
+
+const count: uint = 5
+var stop_me = false
+
+for i in countdown(count, 0):
+  echo i
+  if stop_me: break
+  if i == 0:
+    echo "it should stop now"
+    stop_me = true