Index: clang/lib/Format/TokenAnnotator.cpp
===================================================================
--- clang/lib/Format/TokenAnnotator.cpp
+++ clang/lib/Format/TokenAnnotator.cpp
@@ -3294,6 +3294,10 @@
     return Right.WhitespaceRange.getBegin() != Right.WhitespaceRange.getEnd();
   };
 
+  // If the token is finalized don't touch it (as it could be in a clang-format-off section).
+  if (Left.Finalized)
+      return HasExistingWhitespace();
+
   if (Right.Tok.getIdentifierInfo() && Left.Tok.getIdentifierInfo())
     return true; // Never ever merge two identifiers.
 
Index: clang/unittests/Format/FormatTest.cpp
===================================================================
--- clang/unittests/Format/FormatTest.cpp
+++ clang/unittests/Format/FormatTest.cpp
@@ -21172,6 +21172,22 @@
   verifyFormat("A< A< int > >();", Spaces);
   verifyFormat("A<A<int > >();", Spaces);
   verifyFormat("A< A< int>>();", Spaces);
+
+  Spaces.SpacesInAngles = FormatStyle::SIAS_Always;
+  EXPECT_EQ("// clang-format off\n"
+            "foo<<<1, 1>>>();\n"
+            "// clang-format on\n",
+            format("// clang-format off\n"
+                   "foo<<<1, 1>>>();\n"
+                   "// clang-format on\n",
+                   Spaces));
+  EXPECT_EQ("// clang-format off\n"
+            "foo< < <1, 1> > >();\n"
+            "// clang-format on\n",
+            format("// clang-format off\n"
+                   "foo< < <1, 1> > >();\n"
+                   "// clang-format on\n",
+                   Spaces));
 }
 
 TEST_F(FormatTest, SpaceAfterTemplateKeyword) {