diff --git a/pkgs/racket-test-core/tests/racket/number.rktl b/pkgs/racket-test-core/tests/racket/number.rktl
index 2dd6b1d863..81da9b354a 100644
--- a/pkgs/racket-test-core/tests/racket/number.rktl
+++ b/pkgs/racket-test-core/tests/racket/number.rktl
@@ -2507,6 +2507,7 @@
 (test 10.0+0.0i string->number (string-append "#i1" (make-string 8000 #\0) "/" "1" (make-string 7998 #\0) "#@0"))
 (test 1 string->number (string-append "1" (make-string 8000 #\0) "/" "1" (make-string 8000 #\0) "@0"))
 (test 10.0 string->number (string-append "1" (make-string 8000 #\0) "/" "1" (make-string 7998 #\0) "#@0"))
+(test #f zero? (string->number "7.4109846876187e-323"))
 
 (test #t andmap (lambda (x) (and (>= x 0) (< x 10))) (map random '(10 10 10 10)))
 (test (void) random-seed 5)
diff --git a/racket/src/expander/read/number.rkt b/racket/src/expander/read/number.rkt
index f8ebbd031f..463c5a8dab 100644
--- a/racket/src/expander/read/number.rkt
+++ b/racket/src/expander/read/number.rkt
@@ -210,7 +210,7 @@
                             exp))
      (cond
        [(eqv? n 0) (if (fx= sgn/z -1) (- 0.0) 0.0)]
-       [(approx-expt . > . precision) +inf.0]
+       [(approx-expt . > . precision) (if (fx= sgn/z -1) -inf.0 +inf.0)]
        [(approx-expt . < . (- precision)) (if (fx= sgn/z -1) (- 0.0) 0.0)]
        [else
         (* n (expt radix exp))])]
@@ -224,19 +224,31 @@
        [(state-has-first-half? state) #f]
        [(eqv? n 0) (if (fx= sgn 1) 0.0 (- 0.0))]
        [(and (fixnum? n)
-             ((integer-length n) . < . 50))
+             (n . < . (expt 2 50))
+             (n . > . (- (expt 2 50))))
         ;; No loss of precision in mantissa from early flonum conversion
         (let ([exp (+ exp (* sgn2 exp2))]
               [m (fx->fl (if (fx= sgn -1)
                              (fx- 0 n)
-                             n))]
-              [radix (if (fx= radix 10)
-                         10.0
-                         (fx->fl radix))])
+                             n))])
           (cond
             [(eqv? exp 0) m]
-            [(exp . < . 0) (/ m (expt radix (- exp)))]
-            [else (* m (expt radix exp))]))]
+            [(not (fixnum? exp)) #f]
+            [else
+             (define fradix (if (fx= radix 10)
+                                10.0
+                                (fx->fl radix)))
+             (cond
+               [(exp . fx< . 0)
+                ;; Stay well away from limits on the exponent to make
+                ;; sure there's still no loss of precision. We could
+                ;; use `(integer-length n)` to improve the bounds,
+                ;; but this seems good enough for the common case.
+                (and (exp . fx> . (cond
+                                    [(radix . fx<= . 10) -300]
+                                    [else -240]))
+                     (/ m (expt fradix (fx- 0 exp))))]
+               [else (* m (expt fradix exp))])]))]
        [else #f])]
     [else #f]))
 
diff --git a/racket/src/racket/src/startup.inc b/racket/src/racket/src/startup.inc
index c5be87a000..9e09d2d3e9 100644
--- a/racket/src/racket/src/startup.inc
+++ b/racket/src/racket/src/startup.inc
@@ -54065,7 +54065,7 @@ static const char *startup_source =
 "(if(eqv? n_0 0)"
 "(let-values()(if(fx= sgn/z_0 -1)(- 0.0) 0.0))"
 "(if(> approx-expt_0 precision_0)"
-"(let-values() +inf.0)"
+"(let-values()(if(fx= sgn/z_0 -1) -inf.0 +inf.0))"
 "(if(< approx-expt_0(- precision_0))"
 "(let-values()(if(fx= sgn/z_0 -1)(- 0.0) 0.0))"
 "(let-values()(* n_0(expt radix_0 exp_0)))))))))))"
@@ -54086,16 +54086,22 @@ static const char *startup_source =
 "(let-values() #f)"
 "(if(eqv? n_0 0)"
 "(let-values()(if(fx= sgn_0 1) 0.0(- 0.0)))"
-"(if(if(fixnum? n_0)(<(integer-length n_0) 50) #f)"
+"(if(if(fixnum? n_0)(if(< n_0(expt 2 50))(> n_0(-(expt 2 50))) #f) #f)"
 "(let-values()"
 "(let-values(((exp_1)(+ exp_0(* sgn2_0 exp2_0)))"
-"((m_0)(fx->fl(if(fx= sgn_0 -1)(fx- 0 n_0) n_0)))"
-"((radix_1)(if(fx= radix_0 10) 10.0(fx->fl radix_0))))"
+"((m_0)(fx->fl(if(fx= sgn_0 -1)(fx- 0 n_0) n_0))))"
 "(if(eqv? exp_1 0)"
 "(let-values() m_0)"
-"(if(< exp_1 0)"
-"(let-values()(/ m_0(expt radix_1(- exp_1))))"
-"(let-values()(* m_0(expt radix_1 exp_1)))))))"
+"(if(not(fixnum? exp_1))"
+"(let-values() #f)"
+"(let-values()"
+"(let-values(((fradix_0)(if(fx= radix_0 10) 10.0(fx->fl radix_0))))"
+"(if(fx< exp_1 0)"
+"(let-values()"
+"(if(fx> exp_1(if(fx<= radix_0 10)(let-values() -300)(let-values() -240)))"
+"(/ m_0(expt fradix_0(fx- 0 exp_1)))"
+" #f))"
+"(let-values()(* m_0(expt fradix_0 exp_1))))))))))"
 "(let-values() #f)))))"
 "(let-values() #f))))))"
 "(define-values"