diff --git a/collects/compiler/cm.rkt b/collects/compiler/cm.rkt
index 61a598db06..99af78ff8c 100644
--- a/collects/compiler/cm.rkt
+++ b/collects/compiler/cm.rkt
@@ -17,7 +17,9 @@
          manager-skip-file-handler
          file-stamp-in-collection
          file-stamp-in-paths
-         (rename-out [trace manager-trace-handler]))
+         (rename-out [trace manager-trace-handler])
+         get-file-sha1
+         get-compiled-file-sha1)
 
 (define manager-compile-notify-handler (make-parameter void))
 (define trace (make-parameter void))
@@ -79,7 +81,7 @@
                          (or (not date)
                              (zo-date . > . date)))
                     (cons zo-date
-                          (delay (get-compiled-sha1 mode (get-zo-path))))]
+                          (delay (get-compiled-file-sha1 (get-zo-path) mode)))]
                    [date
                     (cons date
                           (delay (get-source-sha1 (get-path))))]
@@ -574,3 +576,11 @@
                             "empty use-compiled-file-paths list: "
                             modes))
     compilation-manager-load-handler))
+
+
+;; Exported:
+(define (get-compiled-file-sha1 path)
+  (try-file-sha1 path (path-replace-suffix path #".dep")))
+
+(define (get-file-sha1 path)
+  (get-source-sha1 path))
diff --git a/collects/scribblings/mzc/make.scrbl b/collects/scribblings/mzc/make.scrbl
index 16d3e38b22..e43143f18b 100644
--- a/collects/scribblings/mzc/make.scrbl
+++ b/collects/scribblings/mzc/make.scrbl
@@ -82,12 +82,13 @@ would create only @filepath{compiled/b_scm.zo} and
 
 In addition to a bytecode file, @|mzc| creates a file
 @filepath{compiled/@nonterm{name}_@nonterm{ext}.dep} that records
-dependencies of the compiled module on other module files.  Using this
-dependency information, a re-compilation request via @|mzc| can
-consult both the source file's timestamp and the timestamps for the
-sources and bytecode of imported modules.  Furthermore, imported
-modules are themselves compiled as necessary, including updating the
-bytecode and dependency files for the imported modules, transitively.
+dependencies of the compiled module on other module files and the
+source file's SHA-1 hash.  Using this dependency information, a
+re-compilation request via @|mzc| can consult both the source file's
+timestamp/hash and the timestamps/hashes for the bytecode of imported
+modules.  Furthermore, imported modules are themselves compiled as
+necessary, including updating the bytecode and dependency files for
+the imported modules, transitively.
 
 Continuing the @exec{mzc a.scm} example from the previous section, the
 @|mzc| creates @filepath{compiled/a_scm.dep},
@@ -96,7 +97,7 @@ the same time as the @filepath{.zo} files. The
 @filepath{compiled/a_scm.dep} file records the dependency of
 @filepath{a.scm} on @filepath{b.scm}, @filepath{c.scm} and the
 @schememodname[scheme] library. If the @filepath{b.scm} file is
-modified (so that its timestamp changes), then running
+modified (so that its timestamp and SHA-1 hash changes), then running
 
 @commandline{mzc a.scm}
 
@@ -153,7 +154,9 @@ file if
         first sub-directory listed in @scheme[use-compiled-file-paths]
         (at the time that
         @scheme[make-compilation-manager-load/use-compiled-handler]
-        was called)}
+        was called), and either no @filepath{.dep} file exists or it
+        records a source-file SHA-1 hash that differs from the current
+        version and source-file SHA-1 hash;}
 
   @item{no @filepath{.dep} file exists next to the @filepath{.zo}
         file;}
@@ -162,19 +165,28 @@ file if
         match the result of @scheme[(version)];}
 
   @item{one of the files listed in the @filepath{.dep} file has a
-        @filepath{.zo} timestamp newer than the one recorded in the
-        @filepath{.dep} file.}
+        @filepath{.zo} timestamp newer than the target @filepath{.zo},
+        and the combined hashes of the dependencies recorded in the
+        @filepath{.dep} file does not match the combined hash recorded
+        in the @filepath{.dep} file.}
 
   ]}
 
 ]
 
+If SHA-1 hashes override a timestamp-based decision to recompile the
+file, then the target @filepath{.zo} file's timestamp is updated to
+the current time.
+
 After the handler procedure compiles a @filepath{.zo} file, it creates
-a corresponding @filepath{.dep} file that lists the current version,
-plus the @filepath{.zo} timestamp for every file that is
+a corresponding @filepath{.dep} file that lists the current version
+and the identification of every file that is directly
 @scheme[require]d by the module in the compiled file. Additional
 dependencies can be installed during compilation via
-@schememodname[compiler/cm-accomplice].
+@schememodname[compiler/cm-accomplice]. The @filepath{.dep} file also
+records the SHA-1 hash of the module's source, and it records a
+combined SHA-1 hash of all of the dependencies that includes their
+recursive dependencies.
 
 The handler caches timestamps when it checks @filepath{.dep} files,
 and the cache is maintained across calls to the same handler. The
@@ -266,6 +278,21 @@ Returns the file-modification date and @scheme[delay]ed hash of
 
  This function is intended for use with @scheme[manager-skip-file-handler].}
 
+
+@defproc[(get-file-sha1 [p path?]) (or/c string? #f)]{
+
+Computes a SHA-1 hash for the file @racket[p]; the result is
+@racket[#f] if @racket[p] cannot be opened.}
+
+
+@defproc[(get-compiled-file-sha1 [p path?]) (or/c string? #f)]{
+
+Computes a SHA-1 hash for the bytecode file @racket[p], appending any
+dependency-describing hash available from a @filepath{.dep} file when
+available (i.e., the suffix on @racket[p] is replaced by
+@filepath{.dep} to locate dependency information). The result is
+@racket[#f] if @racket[p] cannot be opened.}
+
 @; ----------------------------------------------------------------------
 
 @section{Compilation Manager Hook for Syntax Transformers}
diff --git a/collects/scribblings/scribble/scribble.scrbl b/collects/scribblings/scribble/scribble.scrbl
index 3df63292be..79e74e757d 100644
--- a/collects/scribblings/scribble/scribble.scrbl
+++ b/collects/scribblings/scribble/scribble.scrbl
@@ -2,7 +2,7 @@
 @(require scribble/bnf
           "utils.ss")
 
-@title{@bold{Scribble}: PLT Documentation Tool}
+@title{@bold{Scribble}: Racket Documentation Tool}
 
 @author["Matthew Flatt" "Eli Barzilay"]
 
diff --git a/collects/setup/scribble.rkt b/collects/setup/scribble.rkt
index 6f2baa92b3..0520d874ae 100644
--- a/collects/setup/scribble.rkt
+++ b/collects/setup/scribble.rkt
@@ -10,6 +10,7 @@
          scheme/file
          scheme/fasl
          scheme/serialize
+         compiler/cm
          syntax/modread
          scribble/base-render
          scribble/core
@@ -379,37 +380,60 @@
 (define (make-sci-computed sci)
   (lambda () sci))
 
+(define (file-or-directory-modify-seconds/stamp file
+                                                stamp-time stamp-data pos
+                                                get-sha1)
+  (let ([t (file-or-directory-modify-seconds file #f (lambda () +inf.0))])
+    (cond
+     [(t . <= . stamp-time) stamp-time]
+     [(equal? (list-ref stamp-data pos) (get-sha1 file)) stamp-time]
+     [else t])))
+
 (define ((get-doc-info only-dirs latex-dest auto-main? auto-user?
                        with-record-error setup-printf)
          doc)
   (let* ([info-out-file (build-path (or latex-dest (doc-dest-dir doc)) "out.sxref")]
          [info-in-file  (build-path (or latex-dest (doc-dest-dir doc)) "in.sxref")]
+         [stamp-file  (build-path (or latex-dest (doc-dest-dir doc)) "stamp.sxref")]
          [out-file (build-path (doc-dest-dir doc) "index.html")]
          [src-zo (let-values ([(base name dir?) (split-path (doc-src-file doc))])
                    (build-path base "compiled" (path-add-suffix name ".zo")))]
          [renderer (make-renderer latex-dest doc)]
          [can-run? (can-build? only-dirs doc)]
-         [aux-time (max (file-or-directory-modify-seconds
-                         (build-path (collection-path "scribble")
-                                     "compiled"
-                                     (path-add-suffix
-                                      (if latex-dest
-                                        "latex-render.ss"
-                                        "html-render.ss")
-                                      ".zo"))
-                         #f (lambda () -inf.0))
-                        (file-or-directory-modify-seconds
-                         (build-path (collection-path "scribble")
-                                     "scribble.css")
-                         #f (lambda () +inf.0)))]
+         [stamp-time (file-or-directory-modify-seconds stamp-file #f (lambda () -inf.0))]
+         [stamp-data (with-handlers ([exn:fail:filesystem? (lambda (exn) (list "" "" ""))])
+                       (let ([v (call-with-input-file* stamp-file read)])
+                         (if (and (list? v)
+                                  (= 3 (length v))
+                                  (andmap string? v))
+                             v
+                             (list "" "" ""))))]
+         [renderer-path (build-path (collection-path "scribble")
+                                    "compiled"
+                                    (path-add-suffix
+                                     (if latex-dest
+                                         "latex-render.rkt"
+                                         "html-render.rkt")
+                                     ".zo"))]
+         [css-path (build-path (collection-path "scribble")
+                               "scribble.css")]
+         [aux-time (max (file-or-directory-modify-seconds/stamp
+                         renderer-path
+                         stamp-time stamp-data 1
+                         get-compiled-file-sha1)
+                        (file-or-directory-modify-seconds/stamp
+                         css-path
+                         stamp-time stamp-data 2
+                         get-file-sha1))]
          [my-time (file-or-directory-modify-seconds out-file #f (lambda () -inf.0))]
          [info-out-time (file-or-directory-modify-seconds info-out-file #f (lambda () #f))]
          [info-in-time (file-or-directory-modify-seconds info-in-file #f (lambda () #f))]
          [info-time (min (or info-out-time -inf.0) (or info-in-time -inf.0))]
          [vers (send renderer get-serialize-version)]
-         [src-time (max aux-time
-                        (file-or-directory-modify-seconds
-                         src-zo #f (lambda () +inf.0)))]
+         [src-time (file-or-directory-modify-seconds/stamp
+                    src-zo
+                    stamp-time stamp-data 0
+                    get-compiled-file-sha1)]
          [up-to-date?
           (and info-out-time
                info-in-time
@@ -535,6 +559,13 @@
                    (unless latex-dest 
                      (render-time "xref-in" (write-in info)))
                    (set-info-need-in-write?! info #f))
+                 (when (or (stamp-time . < . aux-time)
+                           (stamp-time . < . src-time))
+                   (let ([data (list (get-compiled-file-sha1 src-zo)
+                                     (get-compiled-file-sha1 renderer-path)
+                                     (get-file-sha1 css-path))])
+                     (with-output-to-file stamp-file #:exists 'truncate/replace (lambda () (write data)))
+                     (file-or-directory-modify-seconds stamp-file (max aux-time src-time))))
                  info))))
          (lambda () #f))
         #f))))