diff --git a/scribblings/tbn.scrbl b/scribblings/tbn.scrbl
index cfc3eb8..9bf3145 100644
--- a/scribblings/tbn.scrbl
+++ b/scribblings/tbn.scrbl
@@ -468,6 +468,17 @@ the variables of @racket[tbn].
        'y (tbf/state (hash 'y 0) -1)))
 ]}
 
+@defproc[(normalize-tbn (tbn TBF)) TBN]{
+
+Normalizes @racket[tbn]: for every @racket[TBF/State], removes the
+inputs that are not in the variables of @racket[tbn], and adds missing
+inputs with 0 weight.
+
+@ex[
+(normalize-tbn (hash 'x (tbf/state (hash 'x 2) -1)
+                     'y (tbf/state (hash 'y 3) 1)))
+]}
+
 @section{Miscellaneous utilities}
 
 @defproc[(group-truth-table-by-nai [tt (Listof (Listof Integer))])
diff --git a/tbn.rkt b/tbn.rkt
index 53d3a91..f524cc1 100644
--- a/tbn.rkt
+++ b/tbn.rkt
@@ -11,6 +11,16 @@
 
   (require/typed racket/hash
     [hash-intersect
+     (->* ((HashTable Variable Real))
+          (#:combine (-> Real Real Real))
+          #:rest (HashTable Variable Real)
+          (HashTable Variable Real))]
+    [(hash-intersect hash-intersect/tbn-tbf)
+     (->* ((HashTable Variable TBF/State))
+          (#:combine (-> TBF/State Real Real))
+          #:rest (HashTable Variable Real)
+          (HashTable Variable Real))]
+    [hash-union
      (->* ((HashTable Variable Real))
           (#:combine (-> Real Real Real))
           #:rest (HashTable Variable Real)
@@ -38,7 +48,7 @@
 
    TBN sbn? tbn->network
    parse-org-tbn read-org-tbn read-org-sbn
-   build-tbn-state-graph normalized-tbn?
+   build-tbn-state-graph normalized-tbn? normalize-tbn
    )
 
   (: apply-tbf-to-state (-> TBF (State (U Zero One)) (U Zero One)))
@@ -529,6 +539,33 @@
       (check-false (normalized-tbn?
                     (hash 'x (tbf/state (hash 'x 0 ) -1)
                           'y (tbf/state (hash 'y 0) -1))))))
+
+  (: normalize-tbn (-> TBN TBN))
+  (define (normalize-tbn tbn)
+    (define vars-0 (for/hash : (VariableMapping Real)
+                             ([(x _) (in-hash tbn)])
+                     (values x 0)))
+    (: normalize-tbf (-> TBF/State TBF/State))
+    (define (normalize-tbf tbf)
+      ;; Only keep the inputs which are also the variables of tbn.
+      (define w-pruned (hash-intersect/tbn-tbf
+                        tbn
+                        (tbf/state-w tbf)
+                        #:combine (λ (_ w) w)))
+      ;; Put in the missing inputs with weight 0.
+      (define w-complete
+        (assert-type (hash-union vars-0 w-pruned #:combine (λ (_ w) w))
+                     (VariableMapping Real)))
+      (tbf/state w-complete (tbf/state-θ tbf)))
+    (for/hash : TBN ([(x tbf) (in-hash tbn)])
+      (values x (normalize-tbf tbf))))
+
+  (module+ test
+    (test-case "normalize-tbn"
+      (check-equal? (normalize-tbn (hash 'x (tbf/state (hash 'x 2) -1)
+                                         'y (tbf/state (hash 'y 3) 1)))
+                    (hash 'x (tbf/state (hash 'x 2 'y 0) -1)
+                          'y (tbf/state (hash 'x 0 'y 3) 1)))))
   )
 
 (module+ test