diff --git a/clang/lib/Format/UnwrappedLineFormatter.cpp b/clang/lib/Format/UnwrappedLineFormatter.cpp
index cee84fb1191ab..d4d72f1174c29 100644
--- a/clang/lib/Format/UnwrappedLineFormatter.cpp
+++ b/clang/lib/Format/UnwrappedLineFormatter.cpp
@@ -366,8 +366,7 @@ class LineJoiner {
     // instead of TheLine->First.
 
     if (Style.AllowShortNamespacesOnASingleLine &&
-        TheLine->First->is(tok::kw_namespace) &&
-        TheLine->Last->is(tok::l_brace)) {
+        TheLine->First->is(tok::kw_namespace)) {
       const auto result = tryMergeNamespace(I, E, Limit);
       if (result > 0)
         return result;
@@ -632,24 +631,37 @@ class LineJoiner {
     if (Limit == 0)
       return 0;
 
-    assert(I[1]);
-    const auto &L1 = *I[1];
+    // The merging code is relative to the opening namespace brace, which could
+    // be either on the first or second line due to the brace wrapping rules.
+    const bool OpenBraceWrapped = Style.BraceWrapping.AfterNamespace;
+    const auto *BraceOpenLine = I + OpenBraceWrapped;
+
+    assert(*BraceOpenLine);
+    if (BraceOpenLine[0]->Last->isNot(TT_NamespaceLBrace))
+      return 0;
+
+    if (std::distance(BraceOpenLine, E) <= 2)
+      return 0;
+
+    if (BraceOpenLine[0]->Last->is(tok::comment))
+      return 0;
+
+    assert(BraceOpenLine[1]);
+    const auto &L1 = *BraceOpenLine[1];
     if (L1.InPPDirective != (*I)->InPPDirective ||
         (L1.InPPDirective && L1.First->HasUnescapedNewline)) {
       return 0;
     }
 
-    if (std::distance(I, E) <= 2)
-      return 0;
-
-    assert(I[2]);
-    const auto &L2 = *I[2];
+    assert(BraceOpenLine[2]);
+    const auto &L2 = *BraceOpenLine[2];
     if (L2.Type == LT_Invalid)
       return 0;
 
     Limit = limitConsideringMacros(I + 1, E, Limit);
 
-    if (!nextTwoLinesFitInto(I, Limit))
+    const auto LinesToBeMerged = OpenBraceWrapped + 2;
+    if (!nextNLinesFitInto(I, I + LinesToBeMerged, Limit))
       return 0;
 
     // Check if it's a namespace inside a namespace, and call recursively if so.
@@ -660,17 +672,19 @@ class LineJoiner {
 
       assert(Limit >= L1.Last->TotalLength + 3);
       const auto InnerLimit = Limit - L1.Last->TotalLength - 3;
-      const auto MergedLines = tryMergeNamespace(I + 1, E, InnerLimit);
+      const auto MergedLines =
+          tryMergeNamespace(BraceOpenLine + 1, E, InnerLimit);
       if (MergedLines == 0)
         return 0;
-      const auto N = MergedLines + 2;
+      const auto N = MergedLines + LinesToBeMerged;
       // Check if there is even a line after the inner result.
       if (std::distance(I, E) <= N)
         return 0;
       // Check that the line after the inner result starts with a closing brace
       // which we are permitted to merge into one line.
-      if (I[N]->First->is(tok::r_brace) && !I[N]->First->MustBreakBefore &&
-          I[MergedLines + 1]->Last->isNot(tok::comment) &&
+      if (I[N]->First->is(TT_NamespaceRBrace) &&
+          !I[N]->First->MustBreakBefore &&
+          BraceOpenLine[MergedLines + 1]->Last->isNot(tok::comment) &&
           nextNLinesFitInto(I, I + N + 1, Limit)) {
         return N;
       }
@@ -685,11 +699,11 @@ class LineJoiner {
       return 0;
 
     // Last, check that the third line starts with a closing brace.
-    if (L2.First->isNot(tok::r_brace) || L2.First->MustBreakBefore)
+    if (L2.First->isNot(TT_NamespaceRBrace) || L2.First->MustBreakBefore)
       return 0;
 
-    // If so, merge all three lines.
-    return 2;
+    // If so, merge all lines.
+    return LinesToBeMerged;
   }
 
   unsigned
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index 4d48bcacddead..c7bfbcf3e5d35 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -28430,6 +28430,35 @@ TEST_F(FormatTest, ShortNamespacesOption) {
       "}}} // namespace foo::bar::baz",
       "namespace foo { namespace bar { namespace baz { class qux; } } }",
       Style);
+  Style.FixNamespaceComments = false;
+
+  Style.BreakBeforeBraces = FormatStyle::BS_Custom;
+  Style.BraceWrapping.AfterNamespace = true;
+  verifyFormat("namespace foo { class bar; }", Style);
+  verifyFormat("namespace foo { namespace bar { class baz; } }", Style);
+  verifyFormat("namespace foo\n"
+               "{ // comment\n"
+               "class bar;\n"
+               "}",
+               Style);
+  verifyFormat("namespace foo { class bar; }",
+               "namespace foo {\n"
+               "class bar;\n"
+               "}",
+               Style);
+  verifyFormat("namespace foo\n"
+               "{\n"
+               "namespace bar\n"
+               "{ // comment\n"
+               "class baz;\n"
+               "}\n"
+               "}",
+               Style);
+  verifyFormat("namespace foo // comment\n"
+               "{\n"
+               "class baz;\n"
+               "}",
+               Style);
 }
 
 TEST_F(FormatTest, WrapNamespaceBodyWithEmptyLinesNever) {