Index: clang/lib/Format/WhitespaceManager.cpp
===================================================================
--- clang/lib/Format/WhitespaceManager.cpp
+++ clang/lib/Format/WhitespaceManager.cpp
@@ -14,6 +14,7 @@
 #include "WhitespaceManager.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/Support/Regex.h"
 #include <algorithm>
 
 namespace clang {
@@ -987,11 +988,30 @@
 
     if (i + 1 != e && Changes[i + 1].ContinuesPPDirective)
       ChangeMaxColumn -= 2;
-    // If this comment follows an } in column 0, it probably documents the
-    // closing of a namespace and we don't want to align it.
-    bool FollowsRBraceInColumn0 = i > 0 && Changes[i].NewlinesBefore == 0 &&
-                                  Changes[i - 1].Tok->is(tok::r_brace) &&
-                                  Changes[i - 1].StartOfTokenColumn == 0;
+
+    // Check if a given comment is most likely a comment to end a namespace.
+    auto IsNamespaceComment = [this](llvm::StringRef CommentText) {
+      // The Regex is a subset of what is defined in
+      // NamespaceEndCommentsFixer.cpp validEndComment().
+      static const llvm::Regex NamespaceCommentRegex(
+          "// *(end (of )?)? *(anonymous|unnamed)? *(namespace|[A-Za-z0-9_]+)",
+          llvm::Regex::IgnoreCase);
+      SmallVector<StringRef, 5> Groups;
+      auto Matched = NamespaceCommentRegex.match(CommentText, &Groups);
+      if (!Matched)
+        return false;
+      assert(Groups.size() > 4);
+      StringRef NamespaceText = Groups[4];
+      return NamespaceText.equals_insensitive("namespace") ||
+             llvm::is_contained(Style.NamespaceMacros, NamespaceText);
+    };
+
+    // We don't want to align namespace end comments. To detect that we check
+    // that the comments follows a closing brace, and its comment matches our
+    // heuristic.
+    bool DontAlignThisComment = i > 0 && Changes[i].NewlinesBefore == 0 &&
+                                Changes[i - 1].Tok->is(tok::r_brace) &&
+                                IsNamespaceComment(Changes[i].Tok->TokenText);
     bool WasAlignedWithStartOfNextLine = false;
     if (Changes[i].NewlinesBefore >= 1) { // A comment on its own line.
       unsigned CommentColumn = SourceMgr.getSpellingColumnNumber(
@@ -1011,7 +1031,7 @@
       }
     }
     if (Style.AlignTrailingComments.Kind == FormatStyle::TCAS_Never ||
-        FollowsRBraceInColumn0) {
+        DontAlignThisComment) {
       alignTrailingComments(StartOfSequence, i, MinColumn);
       MinColumn = ChangeMinColumn;
       MaxColumn = ChangeMinColumn;
Index: clang/unittests/Format/FormatTest.cpp
===================================================================
--- clang/unittests/Format/FormatTest.cpp
+++ clang/unittests/Format/FormatTest.cpp
@@ -4034,7 +4034,7 @@
             "#define HEADER_GUARD\n"
             "namespace my_namespace {\n"
             "int i;\n"
-            "} // my_namespace\n"
+            "}      // my_namespace\n"
             "#endif // HEADER_GUARD",
             format("#ifndef HEADER_GUARD\n"
                    " #define HEADER_GUARD\n"
@@ -19219,7 +19219,7 @@
                "      int x;\n"
                "      };\n"
                "    } // namespace b\n"
-               "  }   // namespace a",
+               "  } // namespace a",
                WhitesmithsBraceStyle);
 
   verifyFormat("void f()\n"
Index: clang/unittests/Format/FormatTestComments.cpp
===================================================================
--- clang/unittests/Format/FormatTestComments.cpp
+++ clang/unittests/Format/FormatTestComments.cpp
@@ -68,6 +68,20 @@
     EXPECT_EQ(Code.str(), format(test::messUp(Code), Style));
   }
 
+  void verifyFormat(llvm::StringRef Expected, llvm::StringRef Code,
+                    const FormatStyle &Style = getLLVMStyle()) {
+    EXPECT_EQ(Expected.str(), format(Expected, Style))
+        << "Expected code is not stable";
+    EXPECT_EQ(Expected.str(), format(test::messUp(Code), Style));
+  }
+
+  void verifyFormatWithoutMessUp(llvm::StringRef Expected, llvm::StringRef Code,
+                                 const FormatStyle &Style = getLLVMStyle()) {
+    EXPECT_EQ(Expected.str(), format(Expected, Style))
+        << "Expected code is not stable";
+    EXPECT_EQ(Expected.str(), format(Code, Style));
+  }
+
   void verifyGoogleFormat(llvm::StringRef Code) {
     verifyFormat(Code, getGoogleStyle());
   }
@@ -3076,6 +3090,55 @@
                    Style));
 }
 
+TEST_F(FormatTestComments, DontAlignNamespaceComments) {
+  FormatStyle Style = getLLVMStyle();
+  Style.NamespaceIndentation = FormatStyle::NI_All;
+  Style.NamespaceMacros.push_back("TESTSUITE");
+  Style.ShortNamespaceLines = 0;
+
+  llvm::StringRef Input = "namespace A {\n"
+                          "  TESTSUITE(B) {\n"
+                          "    namespace C {\n"
+                          "      namespace D {} // namespace D\n"
+                          "      std::string Foo = Bar; // Comment\n"
+                          "    }          // namespace C\n"
+                          "  }\n"
+                          "} // NaMeSpAcE A";
+
+  EXPECT_EQ(Style.AlignTrailingComments.Kind, FormatStyle::TCAS_Always);
+  verifyFormat("namespace A {\n"
+               "  TESTSUITE(B) {\n"
+               "    namespace C {\n"
+               "      namespace D {} // namespace D\n"
+               "      std::string Foo = Bar; // Comment\n"
+               "    } // namespace C\n"
+               "  } // TESTSUITE(B)\n"
+               "} // NaMeSpAcE A",
+               Input, Style);
+
+  Style.AlignTrailingComments.Kind = FormatStyle::TCAS_Never;
+  verifyFormat("namespace A {\n"
+               "  TESTSUITE(B) {\n"
+               "    namespace C {\n"
+               "      namespace D {} // namespace D\n"
+               "      std::string Foo = Bar; // Comment\n"
+               "    } // namespace C\n"
+               "  } // TESTSUITE(B)\n"
+               "} // NaMeSpAcE A",
+               Input, Style);
+
+  Style.AlignTrailingComments.Kind = FormatStyle::TCAS_Leave;
+  verifyFormatWithoutMessUp("namespace A {\n"
+                            "  TESTSUITE(B) {\n"
+                            "    namespace C {\n"
+                            "      namespace D {} // namespace D\n"
+                            "      std::string Foo = Bar; // Comment\n"
+                            "    }          // namespace C\n"
+                            "  }// TESTSUITE(B)\n"
+                            "} // NaMeSpAcE A",
+                            Input, Style);
+}
+
 TEST_F(FormatTestComments, AlignsBlockCommentDecorations) {
   EXPECT_EQ("/*\n"
             " */",