diff --git a/clang/lib/Format/UnwrappedLineFormatter.cpp b/clang/lib/Format/UnwrappedLineFormatter.cpp
--- a/clang/lib/Format/UnwrappedLineFormatter.cpp
+++ b/clang/lib/Format/UnwrappedLineFormatter.cpp
@@ -113,13 +113,14 @@
       } else if (RootToken.isObjCAccessSpecifier()) {
         return true;
       }
-      // Handle Qt signals.
-      else if ((RootToken.isOneOf(Keywords.kw_signals, Keywords.kw_qsignals) &&
-                RootToken.Next && RootToken.Next->is(tok::colon))) {
+      // Handle Qt signals and custom attributes.
+      else if (RootToken.isOneOf(Keywords.kw_signals, Keywords.kw_qsignals) &&
+               RootToken.Next && RootToken.Next->is(tok::colon)) {
         return true;
-      } else if (RootToken.Next &&
-                 RootToken.Next->isOneOf(Keywords.kw_slots,
-                                         Keywords.kw_qslots) &&
+      } else if (RootToken.isAccessSpecifier(/*colonRequired=*/false) &&
+                 RootToken.Next &&
+                 RootToken.Next->isOneOf(Keywords.kw_slots, Keywords.kw_qslots,
+                                         tok::identifier) &&
                  RootToken.Next->Next && RootToken.Next->Next->is(tok::colon)) {
         return true;
       }
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
@@ -3087,6 +3087,10 @@
   // Understand Qt's slots.
   if (FormatTok->isOneOf(Keywords.kw_slots, Keywords.kw_qslots))
     nextToken();
+  // Handle custom attributes.
+  if (FormatTok->is(tok::identifier) && Tokens->peekNextToken()->is(tok::colon))
+    nextToken();
+
   // Otherwise, we don't know what it is, and we'd better keep the next token.
   if (FormatTok->is(tok::colon)) {
     nextToken();
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
@@ -3300,8 +3300,19 @@
                "Q_SIGNALS:\n"
                "  void g2();\n"
                "};");
+  verifyFormat("class A {\n"
+               "public ATTR:\n"
+               "  void f1() {}\n"
+               "protected ATTR:\n"
+               "  void f2() {}\n"
+               "private ATTR:\n"
+               "  void f3() {}\n"
+               "};");
 
   // Don't interpret 'signals' the wrong way.
+  verifyFormat("struct Bitfields {\n"
+               "  unsigned signals : 1;\n"
+               "};");
   verifyFormat("signals.set();");
   verifyFormat("for (Signals signals : f()) {\n}");
   verifyFormat("{\n"
@@ -3311,6 +3322,21 @@
                "label:\n"
                "  signals.baz();\n"
                "}");
+
+  // Don't interpret 'slots' the wrong way.
+  verifyFormat("struct Bitfields {\n"
+               "  unsigned slots : 1;\n"
+               "};");
+  verifyFormat("slots.set();");
+  verifyFormat("for (Signals slots : f()) {\n}");
+  verifyFormat("{\n"
+               "  slots.set(); // This needs indentation.\n"
+               "}");
+  verifyFormat("void f() {\n"
+               "label:\n"
+               "  slots.baz();\n"
+               "}");
+
   verifyFormat("private[1];");
   verifyFormat("testArray[public] = 1;");
   verifyFormat("public();");