diff --git a/dynamics.rkt b/dynamics.rkt
index d40bcab..289c177 100644
--- a/dynamics.rkt
+++ b/dynamics.rkt
@@ -29,11 +29,10 @@
     (: build-state-graph/annotated (-> (Listof State) Graph))
     (define/abstract/error (build-state-graph/annotated sts))
 
-    (: build-state-graph* (-> (Listof State) (U Integer 'full) Graph))
+    (: build-state-graph* (-> (Listof State) (U Positive-Integer 'full) Graph))
     (define/abstract/error (build-state-graph* sts nsteps))
 
-    (: build-state-graph*/annotated (-> (Listof State) (U Integer 'full) Graph))
-    ;; TODO: Integer -> Positive-Integer
+    (: build-state-graph*/annotated (-> (Listof State) (U Positive-Integer 'full) Graph))
     (define/public (build-state-graph*/annotated sts nsteps)
       (define (all-steps-done? k)
         (if (equal? nsteps 'full)
diff --git a/scribblings/dynamics.scrbl b/scribblings/dynamics.scrbl
index 68595e9..b762474 100644
--- a/scribblings/dynamics.scrbl
+++ b/scribblings/dynamics.scrbl
@@ -87,7 +87,9 @@ step/annotated].
 
 }
 
-@defmethod[(build-state-graph* [sts (Listof State)] [nsteps (U Integer 'full)]) Graph]{
+@defmethod[(build-state-graph* [sts (Listof State)]
+			       [nsteps (U Positive-Integer 'full)])
+			       Graph]{
 
 Given a set of starting states and a number @racket[nsteps] of steps to run,
 produces the state graph reachable from the starting states @racket[nsteps]
@@ -98,7 +100,8 @@ This method falls back to exploring the state graph with @method[dds% step].
 
 }
 
-@defmethod[(build-state-graph*/annotated [sts (Listof State)] [nsteps Integer])
+@defmethod[(build-state-graph*/annotated [sts (Listof State)]
+					 [nsteps (U Positive-Integer 'full)])
 					 Graph]{
 
 Given a set of starting states and a number @racket[nsteps] of steps to run,