diff --git a/collects/compiler/private/xform.ss b/collects/compiler/private/xform.ss
index efe7fbb284..db91f70d81 100644
--- a/collects/compiler/private/xform.ss
+++ b/collects/compiler/private/xform.ss
@@ -459,7 +459,7 @@
         (define recorded-cpp-in
           (and precompiled-header
                (open-input-file (change-suffix precompiled-header #".e"))))
-        (define re:boring #rx#"^(?:(?:)|(?:# .*)|(?:#line .*)|(?:#pragma implementation.*)|(?:#pragma interface.*)|(?:#pragma once)|(?:#pragma warning.*))$")
+        (define re:boring #rx#"^(?:(?:[ \t]*)|(?:# .*)|(?:#line .*)|(?:#pragma implementation.*)|(?:#pragma interface.*)|(?:#pragma once)|(?:#pragma warning.*))$")
         (define (skip-to-interesting-line p)
           (let ([l (read-bytes-line p 'any)])
             (cond