diff --git a/clang/lib/Format/BreakableToken.cpp b/clang/lib/Format/BreakableToken.cpp
--- a/clang/lib/Format/BreakableToken.cpp
+++ b/clang/lib/Format/BreakableToken.cpp
@@ -101,17 +101,37 @@
   StringRef::size_type SpaceOffset = Text.find_last_of(Blanks, MaxSplitBytes);
 
   static const auto kNumberedListRegexp = llvm::Regex("^[1-9][0-9]?\\.");
+  // Some spaces are unacceptable to break on, rewind past them.
   while (SpaceOffset != StringRef::npos) {
+    // If a line-comment ends with `\`, the next line continues the comment,
+    // whether or not it starts with `//`. This is confusing and triggers
+    // -Wcomment.
+    // Avoid introducing multiline comments by not allowing a break right
+    // after '\'.
+    if (Style.isCpp()) {
+      StringRef::size_type LastNonBlank =
+          Text.find_last_not_of(Blanks, SpaceOffset);
+      if (LastNonBlank != StringRef::npos && Text[LastNonBlank] == '\\') {
+        SpaceOffset = Text.find_last_of(Blanks, LastNonBlank);
+        continue;
+      }
+    }
+
     // Do not split before a number followed by a dot: this would be interpreted
     // as a numbered list, which would prevent re-flowing in subsequent passes.
-    if (kNumberedListRegexp.match(Text.substr(SpaceOffset).ltrim(Blanks)))
+    if (kNumberedListRegexp.match(Text.substr(SpaceOffset).ltrim(Blanks))) {
       SpaceOffset = Text.find_last_of(Blanks, SpaceOffset);
+      continue;
+    }
+
     // Avoid ever breaking before a { in JavaScript.
-    else if (Style.Language == FormatStyle::LK_JavaScript &&
-             SpaceOffset + 1 < Text.size() && Text[SpaceOffset + 1] == '{')
+    if (Style.Language == FormatStyle::LK_JavaScript &&
+        SpaceOffset + 1 < Text.size() && Text[SpaceOffset + 1] == '{') {
       SpaceOffset = Text.find_last_of(Blanks, SpaceOffset);
-    else
-      break;
+      continue;
+    }
+
+    break;
   }
 
   if (SpaceOffset == StringRef::npos ||
diff --git a/clang/unittests/Format/FormatTestComments.cpp b/clang/unittests/Format/FormatTestComments.cpp
--- a/clang/unittests/Format/FormatTestComments.cpp
+++ b/clang/unittests/Format/FormatTestComments.cpp
@@ -745,6 +745,24 @@
                    getLLVMStyleWithColumns(49)));
 }
 
+TEST_F(FormatTestComments, DontIntroduceMultilineComments) {
+  // Avoid introducing a multiline comment by breaking after `\`.
+  for (int ColumnLimit = 15; ColumnLimit <= 17; ++ColumnLimit) {
+    EXPECT_EQ(
+        "// aaaaaaaaaa\n"
+        "// \\ bb",
+        format("// aaaaaaaaaa \\ bb", getLLVMStyleWithColumns(ColumnLimit)));
+    EXPECT_EQ(
+        "// aaaaaaaaa\n"
+        "// \\  bb",
+        format("// aaaaaaaaa \\  bb", getLLVMStyleWithColumns(ColumnLimit)));
+    EXPECT_EQ(
+        "// aaaaaaaaa\n"
+        "// \\  \\ bb",
+        format("// aaaaaaaaa \\  \\ bb", getLLVMStyleWithColumns(ColumnLimit)));
+  }
+}
+
 TEST_F(FormatTestComments, DontSplitLineCommentsWithPragmas) {
   FormatStyle Pragmas = getLLVMStyleWithColumns(30);
   Pragmas.CommentPragmas = "^ IWYU pragma:";