diff --git a/janet/validate.janet b/janet/validate.janet
index ca1e408..33b7472 100644
--- a/janet/validate.janet
+++ b/janet/validate.janet
@@ -13,7 +13,7 @@ Tracking here, before I start writing this code, the kinds of validation we're h
 * [x] recur not called outside of `loop` forms
 * [x] `loop` form arity checking
 * [x] arity checking of explicit named function calls
-* [ ] flag tail calls
+* [x] flag tail calls
 
 Imports are for a later iteration of Ludus:
 * [ ] no circular imports DEFERRED
@@ -290,7 +290,14 @@ Imports are for a later iteration of Ludus:
 (defn- pkg-root [validator])
 
 # * [ ] flag tail calls (where last term is not-partial args)
-(defn- tail-call [validator])
+(defn- tail-call [validator]
+ (def ast (validator :ast))
+ (when (ast :partial) (break validator))
+ (def status (validator :status))
+ (when (not (status :tail)) (break validator))
+ (def data (ast :data))
+ (def args (last data))
+ (set (args :tail-call) true))
 
 # * [ ] arity checking if first term is name that resolves to a function and args aren't partial
 # XXX: now just check number of args against arity map
@@ -579,16 +586,16 @@ Imports are for a later iteration of Ludus:
 (do
 #(comment
 (def source `
-fn foo {
- () -> :bar
- (x) -> :foo
- (x, y, ...z) -> :baz
+fn bar () -> :bar
+fn foo () -> match :foo with {
+ a -> bar ()
+ b -> :baz
 }
-foo (4)
 `)
 (def scanned (s/scan source))
 (def parsed (p/parse scanned))
 (def validator (new-validator parsed))
 (pp validator)
-((validate validator) :errors)
+(validate validator) 
+(pp parsed)
 )