diff --git a/clang/lib/Format/UnwrappedLineParser.cpp b/clang/lib/Format/UnwrappedLineParser.cpp
--- a/clang/lib/Format/UnwrappedLineParser.cpp
+++ b/clang/lib/Format/UnwrappedLineParser.cpp
@@ -3549,7 +3549,9 @@
 
 void UnwrappedLineParser::readToken(int LevelDifference) {
   SmallVector<FormatToken *, 1> Comments;
+  bool FirstNonCommentOnLine = true;
   do {
+    FormatToken *Previous = FormatTok;
     FormatTok = Tokens->getNextToken();
     assert(FormatTok);
     while (FormatTok->getType() == TT_ConflictStart ||
@@ -3565,8 +3567,17 @@
       FormatTok->MustBreakBefore = true;
     }
 
+    bool FirstOnLine = FormatTok->HasUnescapedNewline || FormatTok->IsFirst;
+    if (Previous && Previous->Tok.is(tok::comment)) {
+      // Consider preprocessor directives preceded by block comments as first on
+      // line.
+      FirstNonCommentOnLine |= FirstOnLine;
+    } else {
+      FirstNonCommentOnLine = FirstOnLine;
+    }
+
     while (!Line->InPPDirective && FormatTok->Tok.is(tok::hash) &&
-           (FormatTok->HasUnescapedNewline || FormatTok->IsFirst)) {
+           FirstNonCommentOnLine) {
       distributeComments(Comments, FormatTok);
       Comments.clear();
       // If there is an unfinished unwrapped line, we flush the preprocessor
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -1797,6 +1797,7 @@
 
 TEST_F(FormatTest, UnderstandsMacros) {
   verifyFormat("#define A (parentheses)");
+  verifyFormat("/* comment */ #define A (parentheses)");
   verifyFormat("#define true ((int)1)");
   verifyFormat("#define and(x)");
   verifyFormat("#define if(x) x");