diff --git a/src/linter/CMakeLists.txt b/src/linter/CMakeLists.txt
index 1e125b5..0d0d177 100644
--- a/src/linter/CMakeLists.txt
+++ b/src/linter/CMakeLists.txt
@@ -7,6 +7,7 @@ noa_library(NAMESPACE sourcemeta PROJECT alterschema NAME linter
     # Antipattern
     antipattern/const_with_type.h
     antipattern/duplicate_enum_values.h
+    antipattern/duplicate_required_values.h
     antipattern/enum_with_type.h
 
     # Simplify
diff --git a/src/linter/antipattern/duplicate_required_values.h b/src/linter/antipattern/duplicate_required_values.h
new file mode 100644
index 0000000..bf49572
--- /dev/null
+++ b/src/linter/antipattern/duplicate_required_values.h
@@ -0,0 +1,31 @@
+class DuplicateRequiredValues final : public Rule {
+public:
+  DuplicateRequiredValues()
+      : Rule("duplicate_required_values",
+             "Setting duplicate values in `required` is considered an "
+             "anti-pattern") {};
+
+  [[nodiscard]] auto
+  condition(const sourcemeta::jsontoolkit::JSON &schema, const std::string &,
+            const std::set<std::string> &vocabularies,
+            const sourcemeta::jsontoolkit::Pointer &) const -> bool override {
+    return contains_any(
+               vocabularies,
+               {"https://json-schema.org/draft/2020-12/vocab/validation",
+                "https://json-schema.org/draft/2019-09/vocab/validation",
+                "http://json-schema.org/draft-07/schema#",
+                "http://json-schema.org/draft-06/schema#",
+                "http://json-schema.org/draft-04/schema#"}) &&
+           schema.is_object() && schema.defines("required") &&
+           schema.at("required").is_array() && !schema.at("required").unique();
+  }
+
+  auto transform(Transformer &transformer) const -> void override {
+    auto collection = transformer.schema().at("required");
+    std::sort(collection.as_array().begin(), collection.as_array().end());
+    auto last =
+        std::unique(collection.as_array().begin(), collection.as_array().end());
+    collection.erase(last, collection.as_array().end());
+    transformer.replace({"required"}, std::move(collection));
+  }
+};
diff --git a/src/linter/linter.cc b/src/linter/linter.cc
index 7e60f79..050e9d5 100644
--- a/src/linter/linter.cc
+++ b/src/linter/linter.cc
@@ -18,6 +18,7 @@ auto contains_any(const T &container, const T &values) -> bool {
 // AntiPattern
 #include "antipattern/const_with_type.h"
 #include "antipattern/duplicate_enum_values.h"
+#include "antipattern/duplicate_required_values.h"
 #include "antipattern/enum_with_type.h"
 // Simplify
 #include "simplify/single_type_array.h"
@@ -46,6 +47,7 @@ auto add(Bundle &bundle, const LinterCategory category) -> void {
     case LinterCategory::AntiPattern:
       bundle.add<EnumWithType>();
       bundle.add<DuplicateEnumValues>();
+      bundle.add<DuplicateRequiredValues>();
       bundle.add<ConstWithType>();
       break;
     case LinterCategory::Simplify:
diff --git a/test/linter/2019_09_test.cc b/test/linter/2019_09_test.cc
index 397a02e..8d2c8a8 100644
--- a/test/linter/2019_09_test.cc
+++ b/test/linter/2019_09_test.cc
@@ -568,3 +568,21 @@ TEST(Lint_2019_09, duplicate_enum_values_1) {
 
   EXPECT_EQ(document, expected);
 }
+
+TEST(Lint_2019_09, duplicate_required_values_1) {
+  sourcemeta::jsontoolkit::JSON document =
+      sourcemeta::jsontoolkit::parse(R"JSON({
+    "$schema": "https://json-schema.org/draft/2019-09/schema",
+    "required": [ "foo", "bar", "baz", "foo" ]
+  })JSON");
+
+  LINT_AND_FIX(document);
+
+  const sourcemeta::jsontoolkit::JSON expected =
+      sourcemeta::jsontoolkit::parse(R"JSON({
+    "$schema": "https://json-schema.org/draft/2019-09/schema",
+    "required": [ "bar", "baz", "foo" ]
+  })JSON");
+
+  EXPECT_EQ(document, expected);
+}
diff --git a/test/linter/2020_12_test.cc b/test/linter/2020_12_test.cc
index de52011..26d048e 100644
--- a/test/linter/2020_12_test.cc
+++ b/test/linter/2020_12_test.cc
@@ -551,3 +551,21 @@ TEST(Lint_2020_12, duplicate_enum_values_1) {
 
   EXPECT_EQ(document, expected);
 }
+
+TEST(Lint_2020_12, duplicate_required_values_1) {
+  sourcemeta::jsontoolkit::JSON document =
+      sourcemeta::jsontoolkit::parse(R"JSON({
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "required": [ "foo", "bar", "baz", "foo" ]
+  })JSON");
+
+  LINT_AND_FIX(document);
+
+  const sourcemeta::jsontoolkit::JSON expected =
+      sourcemeta::jsontoolkit::parse(R"JSON({
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "required": [ "bar", "baz", "foo" ]
+  })JSON");
+
+  EXPECT_EQ(document, expected);
+}
diff --git a/test/linter/draft4_test.cc b/test/linter/draft4_test.cc
index aeb8f5a..03f6981 100644
--- a/test/linter/draft4_test.cc
+++ b/test/linter/draft4_test.cc
@@ -179,3 +179,21 @@ TEST(Lint_draft4, duplicate_enum_values_4) {
 
   EXPECT_EQ(document, expected);
 }
+
+TEST(Lint_draft4, duplicate_required_values_1) {
+  sourcemeta::jsontoolkit::JSON document =
+      sourcemeta::jsontoolkit::parse(R"JSON({
+    "$schema": "http://json-schema.org/draft-04/schema#",
+    "required": [ "foo", "bar", "baz", "foo" ]
+  })JSON");
+
+  LINT_AND_FIX(document);
+
+  const sourcemeta::jsontoolkit::JSON expected =
+      sourcemeta::jsontoolkit::parse(R"JSON({
+    "$schema": "http://json-schema.org/draft-04/schema#",
+    "required": [ "bar", "baz", "foo" ]
+  })JSON");
+
+  EXPECT_EQ(document, expected);
+}
diff --git a/test/linter/draft6_test.cc b/test/linter/draft6_test.cc
index 04608d1..b4a2a1d 100644
--- a/test/linter/draft6_test.cc
+++ b/test/linter/draft6_test.cc
@@ -216,3 +216,21 @@ TEST(Lint_draft6, duplicate_enum_values_6) {
 
   EXPECT_EQ(document, expected);
 }
+
+TEST(Lint_draft6, duplicate_required_values_1) {
+  sourcemeta::jsontoolkit::JSON document =
+      sourcemeta::jsontoolkit::parse(R"JSON({
+    "$schema": "http://json-schema.org/draft-06/schema#",
+    "required": [ "foo", "bar", "baz", "foo" ]
+  })JSON");
+
+  LINT_AND_FIX(document);
+
+  const sourcemeta::jsontoolkit::JSON expected =
+      sourcemeta::jsontoolkit::parse(R"JSON({
+    "$schema": "http://json-schema.org/draft-06/schema#",
+    "required": [ "bar", "baz", "foo" ]
+  })JSON");
+
+  EXPECT_EQ(document, expected);
+}
diff --git a/test/linter/draft7_test.cc b/test/linter/draft7_test.cc
index cea1be8..ecbab33 100644
--- a/test/linter/draft7_test.cc
+++ b/test/linter/draft7_test.cc
@@ -307,3 +307,21 @@ TEST(Lint_draft7, duplicate_enum_values_7) {
 
   EXPECT_EQ(document, expected);
 }
+
+TEST(Lint_draft7, duplicate_required_values_1) {
+  sourcemeta::jsontoolkit::JSON document =
+      sourcemeta::jsontoolkit::parse(R"JSON({
+    "$schema": "http://json-schema.org/draft-07/schema#",
+    "required": [ "foo", "bar", "baz", "foo" ]
+  })JSON");
+
+  LINT_AND_FIX(document);
+
+  const sourcemeta::jsontoolkit::JSON expected =
+      sourcemeta::jsontoolkit::parse(R"JSON({
+    "$schema": "http://json-schema.org/draft-07/schema#",
+    "required": [ "bar", "baz", "foo" ]
+  })JSON");
+
+  EXPECT_EQ(document, expected);
+}