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
@@ -459,6 +459,17 @@
       ++ReadTokens;
     } while (NextTok->is(tok::comment));
 
+    // Skip over preprocessor lines, otherwise we may not
+    // properly diagnose the block as a braced intializer
+    // if the comma separator appears after the pp directive.
+    if (NextTok->is(tok::hash)) {
+      ScopedMacroState MacroState(*Line, Tokens, NextTok);
+      do {
+        NextTok = Tokens->getNextToken();
+        ++ReadTokens;
+      } while (NextTok->isNot(tok::eof));
+    }
+
     switch (Tok->Tok.getKind()) {
     case tok::l_brace:
       if (Style.Language == FormatStyle::LK_JavaScript && PrevTok) {
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 +19268,38 @@
                Style);
 }
 
+TEST_F(FormatTest, ConstructorInitializersWithPreprocessorDirective) {
+  FormatStyle Style = getLLVMStyle();
+  Style.BreakConstructorInitializers = FormatStyle::BCIS_BeforeComma;
+  Style.ConstructorInitializerIndentWidth = 4;
+  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;
+  Style.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_All;
+  verifyFormat("SomeClass::Constructor()\n"
+               ": a{a}\n"
+               "#ifdef CONDITION\n"
+               ", b{b}\n"
+               "#else\n"
+               ", c{c}\n"
+               "#endif\n"
+               ", d{d} {\n}",
+               Style);
+}
+
 TEST_F(FormatTest, Destructors) {
   verifyFormat("void F(int &i) { i.~int(); }");
   verifyFormat("void F(int &i) { i->~int(); }");