Index: clang-tools-extra/clang-tidy/modernize/UseNullptrCheck.cpp
===================================================================
--- clang-tools-extra/clang-tidy/modernize/UseNullptrCheck.cpp
+++ clang-tools-extra/clang-tidy/modernize/UseNullptrCheck.cpp
@@ -45,6 +45,8 @@
       TK_AsIs,
       castExpr(anyOf(ImplicitCastToNull,
                      explicitCastExpr(hasDescendant(ImplicitCastToNull))),
+               // Skip implicit casts to 0 generated by operator<=> rewrites.
+               unless(hasAncestor(cxxRewrittenBinaryOperator())),
                unless(hasAncestor(explicitCastExpr())))
           .bind(CastSequence));
 }
Index: clang-tools-extra/test/clang-tidy/checkers/modernize-use-nullptr-cxx20.cpp
===================================================================
--- /dev/null
+++ clang-tools-extra/test/clang-tidy/checkers/modernize-use-nullptr-cxx20.cpp
@@ -0,0 +1,48 @@
+// RUN: %check_clang_tidy -std=c++20 %s modernize-use-nullptr %t
+
+// Not all systems have #include <compare> to define std::std_ordering
+// required by operator<=>, so recreate minimal version for tests below.
+namespace std {
+
+struct strong_ordering {
+  static const strong_ordering less;
+  static const strong_ordering equal;
+  static const strong_ordering greater;
+  using zero_type = decltype(nullptr);
+
+  friend constexpr bool operator<(const strong_ordering value, zero_type) noexcept {
+    return value.comparison_value < 0;
+  }
+
+  friend constexpr bool operator>(const strong_ordering value, zero_type) noexcept {
+    return value.comparison_value > 0;
+  }
+
+  friend constexpr bool operator>=(const strong_ordering value, zero_type) noexcept {
+    return value.comparison_value >= 0;
+  }
+
+  signed char comparison_value;
+};
+
+inline constexpr strong_ordering strong_ordering::less{-1};
+inline constexpr strong_ordering strong_ordering::equal{0};
+inline constexpr strong_ordering strong_ordering::greater{1};
+
+} // namespace std
+
+class A {
+public:
+  auto operator<=>(const A &other) const = default;
+};
+
+void test_cxx_rewritten_binary_ops() {
+  A a1, a2;
+  bool result;
+  // should not change next line to (a1 nullptr a2)
+  result = (a1 < a2);
+  // CHECK-FIXES: result = (a1 < a2);
+  // should not change next line to (a1 nullptr a2)
+  result = (a1 >= a2);
+  // CHECK-FIXES: result = (a1 >= a2);
+}