diff --git a/clang/unittests/Format/FormatTestJS.cpp b/clang/unittests/Format/FormatTestJS.cpp
--- a/clang/unittests/Format/FormatTestJS.cpp
+++ b/clang/unittests/Format/FormatTestJS.cpp
@@ -2692,5 +2692,9 @@
       "}\n");
 }
 
+TEST_F(FormatTestJS, NumericSeparators) {
+  verifyFormat("x = 1_000_000 + 12;", "x = 1_000_000   + 12;");
+}
+
 } // namespace format
 } // end namespace clang