diff --git a/lib/Lex/Lexer.cpp b/lib/Lex/Lexer.cpp
index 65ea5e3..e18953d 100644
--- a/lib/Lex/Lexer.cpp
+++ b/lib/Lex/Lexer.cpp
@@ -3121,10 +3121,13 @@
       // this as "foo / bar" and langauges with Line comments would lex it as
       // "foo".  Check to see if the character after the second slash is a '*'.
       // If so, we will lex that as a "/" instead of the start of a comment.
-      // However, we never do this in -traditional-cpp mode.
-      if ((LangOpts.LineComment ||
-           getCharAndSize(CurPtr+SizeTmp, SizeTmp2) != '*') &&
-          !LangOpts.TraditionalCPP) {
+      // However, we never do this if we are just preprocessing.
+      bool TreatAsComment = LangOpts.LineComment && !LangOpts.TraditionalCPP;
+      if (!TreatAsComment)
+        if (!(PP && PP->isPreprocessedOutput()))
+          TreatAsComment = getCharAndSize(CurPtr+SizeTmp, SizeTmp2) != '*';
+
+      if (TreatAsComment) {
         if (SkipLineComment(Result, ConsumeChar(CurPtr, SizeTmp, Result)))
           return; // There is a token to return.
 
diff --git a/test/Preprocessor/c90.c b/test/Preprocessor/c90.c
index 1d5010d..3b9105f 100644
--- a/test/Preprocessor/c90.c
+++ b/test/Preprocessor/c90.c
@@ -1,4 +1,5 @@
 /* RUN: %clang_cc1 %s -std=c89 -Eonly -verify -pedantic-errors 
+ * RUN: %clang_cc1 %s -std=c89 -E | FileCheck %s
  */
 
 /* PR3919 */
@@ -8,3 +9,7 @@
 
 #define foo3$bar  /* expected-error {{'$' in identifier}} */
 
+/* CHECK-NOT: this comment should be missing
+ * CHECK: {{^}}// this comment should be present{{$}}
+ */
+// this comment should be present
diff --git a/test/Preprocessor/traditional-cpp.c b/test/Preprocessor/traditional-cpp.c
index 5a94c00..0396c9b 100644
--- a/test/Preprocessor/traditional-cpp.c
+++ b/test/Preprocessor/traditional-cpp.c
@@ -78,3 +78,7 @@
 /* CHECK-NOT: {{^}}a b c in skipped block{{$}}
  * CHECK-NOT: {{^}}/* Comments are whitespace too
  */
+
+Preserve URLs: http://clang.llvm.org
+/* CHECK: {{^}}Preserve URLs: http://clang.llvm.org{{$}}
+ */