diff --git a/collects/tests/typed-scheme/optimizer/generic/known-vector-length.rkt b/collects/tests/typed-scheme/optimizer/generic/known-vector-length.rkt
new file mode 100644
index 0000000000..083d8730f1
--- /dev/null
+++ b/collects/tests/typed-scheme/optimizer/generic/known-vector-length.rkt
@@ -0,0 +1,3 @@
+(module known-vector-length typed/scheme #:optimize
+  (require racket/unsafe/ops)
+  (+ 2 (vector-length (ann (vector 1 2) (Vector Integer Integer)))))
diff --git a/collects/tests/typed-scheme/optimizer/hand-optimized/known-vector-length.rkt b/collects/tests/typed-scheme/optimizer/hand-optimized/known-vector-length.rkt
new file mode 100644
index 0000000000..e480939a25
--- /dev/null
+++ b/collects/tests/typed-scheme/optimizer/hand-optimized/known-vector-length.rkt
@@ -0,0 +1,3 @@
+(module known-vector-length typed/scheme #:optimize
+  (require racket/unsafe/ops)
+  (+ 2 (begin (vector 1 2) 2)))
diff --git a/collects/typed-scheme/private/optimize.rkt b/collects/typed-scheme/private/optimize.rkt
index 670cd8ae1b..0cd2c8ae8d 100644
--- a/collects/typed-scheme/private/optimize.rkt
+++ b/collects/typed-scheme/private/optimize.rkt
@@ -231,6 +231,16 @@
            (begin (log-optimization "unary pair" #'op)
                   #'(op.unsafe p.opt)))
 
+  ;; vector-length of a known-length vector
+  (pattern (#%plain-app (~and op (~or (~literal vector-length)
+                                      (~literal unsafe-vector-length)
+                                      (~literal unsafe-vector*-length)))
+                        v:vector-opt-expr)
+           #:with opt
+           (begin (log-optimization "known-length vector" #'op)
+                  (match (type-of #'v)
+                    [(tc-result1: (HeterogenousVector: es))
+                     #`(begin v.opt #,(length es))]))) ; v may have side effects
   ;; we can optimize vector-length on all vectors.
   ;; since the program typechecked, we know the arg is a vector.
   ;; we can optimize no matter what.