diff --git a/collects/framework/private/color.rkt b/collects/framework/private/color.rkt
index 365c48f0ea..1ade5b4ece 100644
--- a/collects/framework/private/color.rkt
+++ b/collects/framework/private/color.rkt
@@ -297,6 +297,14 @@ added get-regions
                        (get-token in in-start-pos in-lexer-mode)
                        (enable-suspend #t)))])
         (unless (eq? 'eof type)
+          (unless (exact-nonnegative-integer? new-token-start)
+            (error 'color:text<%> "expected an exact nonnegative integer for the token start, got ~e" new-token-start))
+          (unless (exact-nonnegative-integer? new-token-end)
+            (error 'color:text<%> "expected an exact nonnegative integer for the token end, got ~e" new-token-end))
+          (unless (exact-nonnegative-integer? backup-delta)
+            (error 'color:text<%> "expected an exact nonnegative integer for the backup delta, got ~e" backup-delta))
+          (unless (0 . < . (- new-token-end new-token-start))
+            (error 'color:text<%> "expected the distance between the start and end position for each token to be positive, but start was ~e and end was ~e" new-token-start new-token-end))
           (enable-suspend #f)
           #; (printf "~a at ~a to ~a\n" lexeme (+ in-start-pos (sub1 new-token-start))
                      (+ in-start-pos (sub1 new-token-end)))
diff --git a/collects/syntax-color/module-lexer.rkt b/collects/syntax-color/module-lexer.rkt
index 50d62272de..82f733a8a8 100644
--- a/collects/syntax-color/module-lexer.rkt
+++ b/collects/syntax-color/module-lexer.rkt
@@ -1,52 +1,65 @@
-#lang scheme/base
-(require scheme/port
+#lang racket/base
+(require racket/port
          "scheme-lexer.rkt")
 
 (provide module-lexer)
 
+;; mode = (or/c #f 'before-lang-line -- 
+;;              'no-lang-line
+;;              (cons lexer mode)
+;;              lexer)
+
+(define count 0)
+
 (define (module-lexer in offset mode)
+  (set! count (+ count 1))
+  (printf "~a ~s\n" count (list 'module-lexer in offset mode))
   (cond
-   [(not mode)
-    ;; Starting out: look for #lang:
-    (let*-values ([(p) (peeking-input-port in)]
-                  [(init) (file-position p)]
-                  [(start-line start-col start-pos) (port-next-location p)])
-      (let ([get-info (with-handlers ([exn:fail? (lambda (exn) 'fail)])
-                        (read-language p (lambda () #f)))]
-            [sync-ports (lambda ()
-                          (read-bytes (- (file-position p) init) in))])
+    [(or (not mode) (eq? mode 'before-lang-line))
+     (define-values (lexeme type data new-token-start new-token-end) (scheme-lexer in))
+     (printf "before-lang-line lexeme ~s type ~s\n" lexeme type)
+     (cond
+       [(or (eq? type 'comment) (eq? type 'whitespace))
+        (values lexeme 'other data new-token-start new-token-end 0 'before-lang-line)]
+       [else
+        ;; look for #lang:
+        (define p (peeking-input-port in))
+        (port-count-lines! p)
+        (define init (file-position p))
+        (define get-info (with-handlers ([exn:fail:read? values]) (read-language p (λ () 'fail))))
+        (printf "get-info ~s\n" get-info)
         (cond
-         [(procedure? get-info)
-          ;; Produce language as first token:
-          (sync-ports)
-          (let-values ([(end-line end-col end-pos) (port-next-location in)])
-            (values
-             "#lang"
-             'other
-             #f
-             start-pos
-             end-pos
-             0
-             (or (let ([v (get-info 'color-lexer #f)])
-                   (and v
-                        (if (procedure-arity-includes? v 3)
-                            (cons v #f)
-                            v)))
-                 scheme-lexer)))]
-         [(eq? 'fail get-info)
-          (sync-ports)
-          (let*-values ([(end-line end-col end-pos) (port-next-location in)])
-            (values #f 'error #f start-pos end-pos 0 scheme-lexer))]
-         [else
-          ;; Start over using the Scheme lexer
-          (module-lexer in offset scheme-lexer)])))]
-   [(pair? mode)
-    ;; #lang-selected language consumes and produces a mode:
-    (let-values ([(lexeme type data new-token-start new-token-end backup-delta new-mode) 
-                  ((car mode) in offset (cdr mode))])
-      (values lexeme type data new-token-start new-token-end backup-delta (cons (car mode) new-mode)))]
-   [else
-    ;; #lang-selected language (or default) doesn't deal with modes:
-    (let-values ([(lexeme type data new-token-start new-token-end) 
-                  (mode in)])
-      (values lexeme type data new-token-start new-token-end 0 mode))]))
+          [(not (procedure? get-info))
+           ;(or (exn? get-info) (eq? get-info 'fail))
+           (values lexeme type data new-token-start new-token-end 0 'no-lang-line)]
+          [(procedure? get-info)
+           (define end-pos (file-position p))
+           (read-bytes (- end-pos init) in) ;; sync ports
+           ;; Produce language as first token:
+           (values
+            "#lang"
+            'other
+            #f
+            1 ;; start-pos
+            (+ end-pos 1)
+            0
+            (or (let ([v (get-info 'color-lexer #f)])
+                  (and v
+                       (if (procedure-arity-includes? v 3)
+                           (cons v #f)
+                           v)))
+                scheme-lexer))])])]
+    [(eq? mode 'no-lang-line)
+     (let-values ([(lexeme type data new-token-start new-token-end) 
+                   (scheme-lexer in)])
+       (values lexeme type data new-token-start new-token-end 0 'no-lang-line))]
+    [(pair? mode)
+     ;; #lang-selected language consumes and produces a mode:
+     (let-values ([(lexeme type data new-token-start new-token-end backup-delta new-mode) 
+                   ((car mode) in offset (cdr mode))])
+       (values lexeme type data new-token-start new-token-end backup-delta (cons (car mode) new-mode)))]
+    [else
+     ;; #lang-selected language (or default) doesn't deal with modes:
+     (let-values ([(lexeme type data new-token-start new-token-end) 
+                   (mode in)])
+       (values lexeme type data new-token-start new-token-end 0 mode))]))