Index: include/llvm/MC/MCParser/AsmLexer.h
===================================================================
--- include/llvm/MC/MCParser/AsmLexer.h
+++ include/llvm/MC/MCParser/AsmLexer.h
@@ -32,7 +32,7 @@
   bool IsAtStartOfLine;
   bool IsAtStartOfStatement;
   bool IsParsingMSInlineAsm;
-
+  bool IsPeeking;
   void operator=(const AsmLexer&) = delete;
   AsmLexer(const AsmLexer&) = delete;
 
Index: lib/MC/MCParser/AsmLexer.cpp
===================================================================
--- lib/MC/MCParser/AsmLexer.cpp
+++ lib/MC/MCParser/AsmLexer.cpp
@@ -34,6 +34,7 @@
   IsAtStartOfLine = true;
   IsAtStartOfStatement = true;
   IsParsingMSInlineAsm = false;
+  IsPeeking = false;
   AllowAtInIdentifier = !StringRef(MAI.getCommentString()).startswith("@");
 }
 
@@ -492,6 +493,8 @@
   bool SavedAtStartOfLine = IsAtStartOfLine;
   bool SavedAtStartOfStatement = IsAtStartOfStatement;
   bool SavedSkipSpace = SkipSpace;
+  bool SavedIsPeeking = IsPeeking;
+  IsPeeking = true;
 
   std::string SavedErr = getErr();
   SMLoc SavedErrLoc = getErrLoc();
@@ -515,7 +518,7 @@
   IsAtStartOfStatement = SavedAtStartOfStatement;
   CurPtr = SavedCurPtr;
   TokStart = SavedTokStart;
-
+  IsPeeking = SavedIsPeeking;
   return ReadCount;
 }
 
@@ -542,7 +545,7 @@
   // This always consumes at least one character.
   int CurChar = getNextChar();
 
-  if (CurChar == '#' && IsAtStartOfStatement) {
+  if (!IsPeeking && CurChar == '#' && IsAtStartOfStatement) {
     // If this starts with a '#', this may be a cpp
     // hash directive and otherwise a line comment.
     AsmToken TokenBuf[2];
Index: test/MC/AsmParser/pr28921.s
===================================================================
--- /dev/null
+++ test/MC/AsmParser/pr28921.s
@@ -0,0 +1,8 @@
+// RUN: llvm-mc -triple i386-unknown-unknown %s
+
+# 1 "kernel.S"
+# 1 "<built-in>" 1
+# 1 "kernel.S" 2
+##
+# 10 "kernel.S"
+##