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
@@ -489,6 +489,17 @@
         if (Style.Language == FormatStyle::LK_Proto) {
           ProbablyBracedList = NextTok->isOneOf(tok::comma, tok::r_square);
         } else {
+          // Skip NextTok over preprocessor lines, otherwise we may not
+          // properly diagnose the block as a braced intializer
+          // if the comma separator appears after the pp directive.
+          while (NextTok->is(tok::hash)) {
+            ScopedMacroState MacroState(*Line, Tokens, NextTok);
+            do {
+              NextTok = Tokens->getNextToken();
+              ++ReadTokens;
+            } while (NextTok->isNot(tok::eof));
+          }
+
           // Using OriginalColumn to distinguish between ObjC methods and
           // binary operators is a bit hacky.
           bool NextIsObjCMethod = NextTok->isOneOf(tok::plus, tok::minus) &&
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
@@ -19268,6 +19268,59 @@
                Style);
 }
 
+TEST_F(FormatTest, ConstructorInitializersWithPreprocessorDirective) {
+  FormatStyle Style = getLLVMStyle();
+  Style.BreakConstructorInitializers = FormatStyle::BCIS_BeforeComma;
+  Style.ConstructorInitializerIndentWidth = 4;
+  verifyFormat("SomeClass::Constructor()\n"
+               "    : a{a}\n"
+               "    , b{b} {}",
+               Style);
+  verifyFormat("SomeClass::Constructor()\n"
+               "    : a{a}\n"
+               "#if CONDITION\n"
+               "    , b{b}\n"
+               "#endif\n"
+               "{\n}",
+               Style);
+  Style.ConstructorInitializerIndentWidth = 2;
+  verifyFormat("SomeClass::Constructor()\n"
+               "#if CONDITION\n"
+               "  : a{a}\n"
+               "#endif\n"
+               "  , b{b}\n"
+               "  , c{c} {\n}",
+               Style);
+  Style.ConstructorInitializerIndentWidth = 0;
+  verifyFormat("SomeClass::Constructor()\n"
+               ": a{a}\n"
+               "#ifdef CONDITION\n"
+               ", b{b}\n"
+               "#else\n"
+               ", c{c}\n"
+               "#endif\n"
+               ", d{d} {\n}",
+               Style);
+  Style.ConstructorInitializerIndentWidth = 4;
+  verifyFormat("SomeClass::Constructor()\n"
+               "    : a{a}\n"
+               "#if WINDOWS\n"
+               "#if DEBUG\n"
+               "    , b{0}\n"
+               "#else\n"
+               "    , b{1}\n"
+               "#endif\n"
+               "#else\n"
+               "#if DEBUG\n"
+               "    , b{2}\n"
+               "#else\n"
+               "    , b{3}\n"
+               "#endif\n"
+               "#endif\n"
+               "{\n}",
+               Style);
+}
+
 TEST_F(FormatTest, Destructors) {
   verifyFormat("void F(int &i) { i.~int(); }");
   verifyFormat("void F(int &i) { i->~int(); }");