diff --git a/hkmc2/shared/src/main/scala/hkmc2/syntax/Parser.scala b/hkmc2/shared/src/main/scala/hkmc2/syntax/Parser.scala
index e0bd732c3..7a6ba4326 100644
--- a/hkmc2/shared/src/main/scala/hkmc2/syntax/Parser.scala
+++ b/hkmc2/shared/src/main/scala/hkmc2/syntax/Parser.scala
@@ -900,7 +900,7 @@ abstract class Parser(
       case (NEWLINE, _) :: (KEYWORD(kw), _) :: _
       if kw.canStartInfixOnNewLine && kw.leftPrecOrMin > prec
       && infixRules.kwAlts.contains(kw.name)
-      && kw != Keyword.`do` // This is to avoid the following case:
+      && (kw isnt Keyword.`do`) // This is to avoid the following case:
         //  ```
         //  0 then "null"
         //  do console.log("non-null")
diff --git a/hkmc2/shared/src/test/mlscript/codegen/While.mls b/hkmc2/shared/src/test/mlscript/codegen/While.mls
index 9b1830199..249d239f9 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/While.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/While.mls
@@ -143,6 +143,14 @@ let i = 0 in while
 //│ > 2
 //│ > 3
 
+let i = 0 in while
+  do log(i)
+  i < 3 do set i += 1
+//│ > 0
+//│ > 1
+//│ > 2
+//│ > 3
+
 
 // * Note that the semantics of UCS-while is quite subtle.
 // * Currently, we only treat the *top-level* `else` as terminating the loop;
@@ -232,6 +240,16 @@ f(Cons(1, Cons(2, Cons(3, 0))))
 //│ > 3
 //│ > Done!
 
+fun f(ls) =
+  while
+    do print(ls)
+    ls is Cons(h, tl) do set ls = tl
+
+f(Cons(1, Cons(2, Cons(3, 0))))
+//│ > Cons(1, Cons(2, Cons(3, 0)))
+//│ > Cons(2, Cons(3, 0))
+//│ > Cons(3, 0)
+//│ > 0
 
 
 // ——— FIXME: ———
@@ -246,7 +264,7 @@ while log("Hello World"); false
   then 0(0)
   else 1
 //│ ╔══[PARSE ERROR] Unexpected 'then' keyword here
-//│ ║  l.246: 	  then 0(0)
+//│ ║  l.264: 	  then 0(0)
 //│ ╙──       	  ^^^^
 //│ ═══[ERROR] Unrecognized term split (false literal).
 //│ ═══[RUNTIME ERROR] Error: match error
diff --git a/hkmc2/shared/src/test/mlscript/ucs/syntax/Do.mls b/hkmc2/shared/src/test/mlscript/ucs/syntax/Do.mls
index 6390900a5..0e42340b3 100644
--- a/hkmc2/shared/src/test/mlscript/ucs/syntax/Do.mls
+++ b/hkmc2/shared/src/test/mlscript/ucs/syntax/Do.mls
@@ -16,6 +16,21 @@ if x do
 x
 //│ = false
 
+if not(x) do
+  print("executed")
+//│ > executed
+
+:e
+:re
+if not of x do
+  print("executed")
+//│ ╔══[ERROR] Unrecognized term split (application).
+//│ ║  l.25: 	if not of x do
+//│ ║        	   ^^^^^^^^^^^
+//│ ║  l.26: 	  print("executed")
+//│ ╙──      	^^^^^^^^^^^^^^^^^^^
+//│ ═══[RUNTIME ERROR] Error: match error
+
 if (not of x) do
   print("executed")
   set x = false
@@ -56,10 +71,10 @@ fun g(y) =
   x
 //│ ╔══[ERROR] Mixed use of `do` and `then` in the `if` expression.
 //│ ╟── Keyword `then` is used here.
-//│ ║  l.55: 	    Some(v) and v % 2 == 0 then set x = Some(v / 2)
+//│ ║  l.70: 	    Some(v) and v % 2 == 0 then set x = Some(v / 2)
 //│ ║        	    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 //│ ╟── Keyword `do` is used here.
-//│ ║  l.54: 	    Some(0) do set x = None
+//│ ║  l.69: 	    Some(0) do set x = None
 //│ ╙──      	    ^^^^^^^^^^^^^^^^^^^^^^^
 
 g(0)