diff --git a/clang/lib/Format/NamespaceEndCommentsFixer.cpp b/clang/lib/Format/NamespaceEndCommentsFixer.cpp
--- a/clang/lib/Format/NamespaceEndCommentsFixer.cpp
+++ b/clang/lib/Format/NamespaceEndCommentsFixer.cpp
@@ -261,7 +261,8 @@
           updateEndComment(EndCommentPrevTok, std::string(), SourceMgr, &Fixes);
         }
         ++CompactedNamespacesCount;
-        AllNamespaceNames = "::" + NamespaceName + AllNamespaceNames;
+        if (!NamespaceName.empty())
+          AllNamespaceNames = "::" + NamespaceName + AllNamespaceNames;
         continue;
       }
       NamespaceName += AllNamespaceNames;
diff --git a/clang/unittests/Format/NamespaceEndCommentsFixerTest.cpp b/clang/unittests/Format/NamespaceEndCommentsFixerTest.cpp
--- a/clang/unittests/Format/NamespaceEndCommentsFixerTest.cpp
+++ b/clang/unittests/Format/NamespaceEndCommentsFixerTest.cpp
@@ -256,6 +256,15 @@
                                     "int j;\n"
                                     "};}",
                                     CompactNamespacesStyle));
+  EXPECT_EQ("namespace out { namespace {\n"
+            "int i;\n"
+            "int j;\n"
+            "}}// namespace out",
+            fixNamespaceEndComments("namespace out { namespace {\n"
+                                    "int i;\n"
+                                    "int j;\n"
+                                    "}}",
+                                    CompactNamespacesStyle));
 
   // Adds an end comment after a semicolon.
   EXPECT_EQ("namespace {\n"
@@ -609,6 +618,11 @@
                                     "}// banamespace in\n"
                                     "} // namespace out",
                                     CompactNamespacesStyle));
+  EXPECT_EQ("namespace out { namespace {\n"
+            "}} // namespace out",
+            fixNamespaceEndComments("namespace out { namespace {\n"
+                                    "}} // namespace out::",
+                                    CompactNamespacesStyle));
 }
 
 TEST_F(NamespaceEndCommentsFixerTest, UpdatesInvalidMacroEndLineComment) {