diff --git a/clang/lib/Tooling/Inclusions/HeaderIncludes.cpp b/clang/lib/Tooling/Inclusions/HeaderIncludes.cpp
--- a/clang/lib/Tooling/Inclusions/HeaderIncludes.cpp
+++ b/clang/lib/Tooling/Inclusions/HeaderIncludes.cpp
@@ -100,7 +100,8 @@
           [](const SourceManager &SM, Lexer &Lex, Token Tok) -> unsigned {
             if (checkAndConsumeDirectiveWithName(Lex, "ifndef", Tok)) {
               skipComments(Lex, Tok);
-              if (checkAndConsumeDirectiveWithName(Lex, "define", Tok))
+              if (checkAndConsumeDirectiveWithName(Lex, "define", Tok) &&
+                  Tok.isAtStartOfLine())
                 return SM.getFileOffset(Tok.getLocation());
             }
             return 0;
diff --git a/clang/unittests/Tooling/HeaderIncludesTest.cpp b/clang/unittests/Tooling/HeaderIncludesTest.cpp
--- a/clang/unittests/Tooling/HeaderIncludesTest.cpp
+++ b/clang/unittests/Tooling/HeaderIncludesTest.cpp
@@ -347,6 +347,18 @@
   EXPECT_EQ(Expected, insert(Code, "<vector>"));
 }
 
+TEST_F(HeaderIncludesTest, FakeHeaderGuardIfnDef) {
+  std::string Code = "#ifndef A_H\n"
+                     "#define A_H 1\n"
+                     "#endif";
+  std::string Expected = "#include \"b.h\"\n"
+                         "#ifndef A_H\n"
+                         "#define A_H 1\n"
+                         "#endif";
+
+  EXPECT_EQ(Expected, insert(Code, "\"b.h\""));
+}
+
 TEST_F(HeaderIncludesTest, HeaderGuardWithComment) {
   std::string Code = "// comment \n"
                      "#ifndef X // comment\n"