diff --git a/pkgs/racket-doc/scribblings/reference/sequences.scrbl b/pkgs/racket-doc/scribblings/reference/sequences.scrbl
index 4891e55e13..d1353b172e 100644
--- a/pkgs/racket-doc/scribblings/reference/sequences.scrbl
+++ b/pkgs/racket-doc/scribblings/reference/sequences.scrbl
@@ -158,8 +158,8 @@ each element in the sequence.
   (sequence? "word")
   (sequence? #\x)]}
 
-@defproc*[([(in-range [end number?]) stream?]
-           [(in-range [start number?] [end number?] [step number? 1]) stream?])]{
+@defproc*[([(in-range [end real?]) stream?]
+           [(in-range [start real?] [end real?] [step real? 1]) stream?])]{
   Returns a sequence (that is also a @tech{stream}) whose elements are
   numbers.  The single-argument case @racket[(in-range end)] is
   equivalent to @racket[(in-range 0 end 1)].  The first number in the
diff --git a/pkgs/racket-test-core/tests/racket/for.rktl b/pkgs/racket-test-core/tests/racket/for.rktl
index ec943ccbe7..ffd8d4c455 100644
--- a/pkgs/racket-test-core/tests/racket/for.rktl
+++ b/pkgs/racket-test-core/tests/racket/for.rktl
@@ -450,7 +450,81 @@
              #rx".*expected number of values not received.*")
 (test 1 'one (begin (for/fold () () (values)) 1))
 
+;; iterator contract tests
+(err/rt-test (for ([x (in-range (sqrt -1))]) x)
+             exn:fail:contract?
+             #rx"expected\\: real\\?")
+(err/rt-test (for ([x (in-range 1 (sqrt -1))]) x)
+             exn:fail:contract?
+             #rx"expected\\: real\\?")
+(err/rt-test (for ([x (in-range 1 2 (sqrt -1))]) x)
+             exn:fail:contract?
+             #rx"expected\\: real\\?")
+(test (* 10 pi) 'in-range-with-reals
+      (for/sum ([x (in-range 0 (+ (* 4 pi) .1) pi)]) x))
+(err/rt-test (for ([x (in-naturals 1.1)]) x)
+             exn:fail:contract?
+             #rx"expected\\: exact-nonnegative-integer\\?")
+(err/rt-test (for ([x (in-naturals -1)]) x)
+             exn:fail:contract?
+             #rx"expected\\: exact-nonnegative-integer\\?")
+(err/rt-test (for ([x (in-list 1)]) x)
+             exn:fail:contract?
+             #rx"expected\\: list\\?")
+(err/rt-test (for ([x (in-list (vector 1 2 3))]) x)
+             exn:fail:contract?
+             #rx"expected\\: list\\?")
+(err/rt-test (for ([x (in-list (mcons 1 '()))]) x)
+             exn:fail:contract?
+             #rx"expected\\: list\\?")
+(err/rt-test (for ([x (in-mlist (list 1 2 3))]) x)
+             exn:fail:contract?
+             #rx"expected\\: mpair\\?")
+(err/rt-test (for ([x (in-vector '(1 2))]) x)
+             exn:fail:contract?
+             #rx"expected\\: vector")
+(err/rt-test (for ([x (in-vector (vector 1 2) -1)]) x)
+             exn:fail:contract?
+             #rx"starting index is out of range")
+(err/rt-test (for ([x (in-vector (vector 1 2) 10)]) x)
+             exn:fail:contract?
+             #rx"starting index is out of range")
+(err/rt-test (for ([x (in-vector (vector 1 2) 1.1)]) x)
+             exn:fail:contract?
+             #rx"expected\\: exact-integer\\?")
+(err/rt-test (for ([x (in-vector (vector 1 2) 0 1.1)]) x)
+             exn:fail:contract?
+             #rx"expected\\: exact-integer\\?")
+(err/rt-test (for ([x (in-vector (vector 1 2) 0 2 1.1)]) x)
+             exn:fail:contract?
+             #rx"expected:.*exact-integer\\?")
+(err/rt-test (for ([x (in-vector (vector 1 2) 0 2 0)]) x)
+             exn:fail:contract?
+             #rx"expected:.*not/c zero\\?")
+(err/rt-test (for ([x (in-port (vector 1 2))]) x)
+             exn:fail:contract?
+             #rx"expected:.*procedure-arity-includes/c 1")
+(err/rt-test (for ([x (in-input-port-bytes (vector 1 2))]) x)
+             exn:fail:contract?
+             #rx"expected: input-port\\?")
+(err/rt-test (for ([x (in-hash (vector 1 2))]) x)
+             exn:fail:contract?
+             #rx"expected: hash\\?")
+(err/rt-test (for ([x (in-hash-pairs (vector 1 2))]) x)
+             exn:fail:contract?
+             #rx"expected: hash\\?")
+(err/rt-test (for ([x (in-hash-keys (vector 1 2))]) x)
+             exn:fail:contract?
+             #rx"expected: hash\\?")
+(err/rt-test (for ([x (in-hash-values (vector 1 2))]) x)
+             exn:fail:contract?
+             #rx"expected: hash\\?")
+(err/rt-test (for ([x (in-hash (hash 1 2))]) x)
+             exn:fail:contract:arity?
+             #rx"expected number of values not received")
+
 ;; for/fold syntax checking
 (syntax-test #'(for/fold () bad 1) #rx".*bad sequence binding clauses.*")
 
+
 (report-errs)
diff --git a/racket/collects/racket/private/for.rkt b/racket/collects/racket/private/for.rkt
index 65b4defe5c..cd85fa3432 100644
--- a/racket/collects/racket/private/for.rkt
+++ b/racket/collects/racket/private/for.rkt
@@ -590,6 +590,7 @@
     (values car cdr l pair? #f #f))
 
   (define (in-mlist l)
+    (unless (mpair? l) (raise-argument-error 'in-mlist "mpair?" l))
     (make-do-sequence (lambda () (:mlist-gen l))))
 
   (define (:mlist-gen l)