diff --git a/lib/rule-tester/flat-rule-tester.js b/lib/rule-tester/flat-rule-tester.js
index 01163c48e4d..c790dab69e7 100644
--- a/lib/rule-tester/flat-rule-tester.js
+++ b/lib/rule-tester/flat-rule-tester.js
@@ -853,6 +853,22 @@ class FlatRuleTester {
             const result = runRuleForItem(item);
             const messages = result.messages;
 
+            for (const message of messages) {
+                if (hasOwnProperty(message, "suggestions")) {
+
+                    /** @type {Map<string, number>} */
+                    const seenMessageIndices = new Map();
+
+                    for (let i = 0; i < message.suggestions.length; i += 1) {
+                        const suggestionMessage = message.suggestions[i].desc;
+                        const previous = seenMessageIndices.get(suggestionMessage);
+
+                        assert.ok(!seenMessageIndices.has(suggestionMessage), `Suggestion message '${suggestionMessage}' reported from suggestion ${i} was previously reported by suggestion ${previous}. Suggestion messages should be unique within an error.`);
+                        seenMessageIndices.set(suggestionMessage, i);
+                    }
+                }
+            }
+
             if (typeof item.errors === "number") {
 
                 if (item.errors === 0) {
diff --git a/lib/rule-tester/rule-tester.js b/lib/rule-tester/rule-tester.js
index 626d9dcd3ce..bd46fcc807a 100644
--- a/lib/rule-tester/rule-tester.js
+++ b/lib/rule-tester/rule-tester.js
@@ -845,6 +845,22 @@ class RuleTester {
             const result = runRuleForItem(item);
             const messages = result.messages;
 
+            for (const message of messages) {
+                if (hasOwnProperty(message, "suggestions")) {
+
+                    /** @type {Map<string, number>} */
+                    const seenMessageIndices = new Map();
+
+                    for (let i = 0; i < message.suggestions.length; i += 1) {
+                        const suggestionMessage = message.suggestions[i].desc;
+                        const previous = seenMessageIndices.get(suggestionMessage);
+
+                        assert.ok(!seenMessageIndices.has(suggestionMessage), `Suggestion message '${suggestionMessage}' reported from suggestion ${i} was previously reported by suggestion ${previous}. Suggestion messages should be unique within an error.`);
+                        seenMessageIndices.set(suggestionMessage, i);
+                    }
+                }
+            }
+
             if (typeof item.errors === "number") {
 
                 if (item.errors === 0) {
diff --git a/tests/fixtures/testers/rule-tester/suggestions.js b/tests/fixtures/testers/rule-tester/suggestions.js
index ecedde04637..57cb84f1653 100644
--- a/tests/fixtures/testers/rule-tester/suggestions.js
+++ b/tests/fixtures/testers/rule-tester/suggestions.js
@@ -59,6 +59,98 @@ module.exports.withMessageIds = {
     }
 };
 
+module.exports.withDuplicateDescriptions = {
+    meta: {
+        hasSuggestions: true
+    },
+    create(context) {
+        return {
+            Identifier(node) {
+                if (node.name === "foo") {
+                    context.report({
+                        node,
+                        message: "Avoid using identifiers name 'foo'.",
+                        suggest: [{
+                            desc: "Rename 'foo' to 'bar'",
+                            fix: fixer => fixer.replaceText(node, "bar")
+                        }, {
+                            desc: "Rename 'foo' to 'bar'",
+                            fix: fixer => fixer.replaceText(node, "baz")
+                        }]
+                    });
+                }
+            }
+        };
+    }
+};
+
+module.exports.withDuplicateMessageIdsNoData = {
+    meta: {
+        messages: {
+            avoidFoo: "Avoid using identifiers named '{{ name }}'.",
+            renameFoo: "Rename identifier"
+        },
+        hasSuggestions: true
+    },
+    create(context) {
+        return {
+            Identifier(node) {
+                if (node.name === "foo") {
+                    context.report({
+                        node,
+                        messageId: "avoidFoo",
+                        data: {
+                            name: "foo"
+                        },
+                        suggest: [{
+                            messageId: "renameFoo",
+                            fix: fixer => fixer.replaceText(node, "bar")
+                        }, {
+                            messageId: "renameFoo",
+                            fix: fixer => fixer.replaceText(node, "baz")
+                        }]
+                    });
+                }
+            }
+        };
+    }
+};
+
+module.exports.withDuplicateMessageIdsWithData = {
+    meta: {
+        messages: {
+            avoidFoo: "Avoid using identifiers named foo.",
+            renameFoo: "Rename identifier 'foo' to '{{ newName }}'"
+        },
+        hasSuggestions: true
+    },
+    create(context) {
+        return {
+            Identifier(node) {
+                if (node.name === "foo") {
+                    context.report({
+                        node,
+                        messageId: "avoidFoo",
+                        suggest: [{
+                            messageId: "renameFoo",
+                            data: {
+                                newName: "bar"
+                            },
+                            fix: fixer => fixer.replaceText(node, "bar")
+                        }, {
+                            messageId: "renameFoo",
+                            data: {
+                                newName: "bar"
+                            },
+                            fix: fixer => fixer.replaceText(node, "baz")
+                        }]
+                    });
+                }
+            }
+        };
+    }
+};
+
 module.exports.withoutHasSuggestionsProperty = {
     create(context) {
         return {
diff --git a/tests/lib/rule-tester/flat-rule-tester.js b/tests/lib/rule-tester/flat-rule-tester.js
index c6d0730b3c6..fe97bd2c851 100644
--- a/tests/lib/rule-tester/flat-rule-tester.js
+++ b/tests/lib/rule-tester/flat-rule-tester.js
@@ -2313,6 +2313,39 @@ describe("FlatRuleTester", () => {
             }, /Invalid suggestion property name 'outpt'/u);
         });
 
+        it("should fail if a rule produces two suggestions with the same description", () => {
+            assert.throws(() => {
+                ruleTester.run("suggestions-with-duplicate-descriptions", require("../../fixtures/testers/rule-tester/suggestions").withDuplicateDescriptions, {
+                    valid: [],
+                    invalid: [
+                        { code: "var foo = bar;", errors: 1 }
+                    ]
+                });
+            }, "Suggestion message 'Rename 'foo' to 'bar'' reported from suggestion 1 was previously reported by suggestion 0. Suggestion messages should be unique within an error.");
+        });
+
+        it("should fail if a rule produces two suggestions with the same messageId without data", () => {
+            assert.throws(() => {
+                ruleTester.run("suggestions-with-duplicate-messageids-no-data", require("../../fixtures/testers/rule-tester/suggestions").withDuplicateMessageIdsNoData, {
+                    valid: [],
+                    invalid: [
+                        { code: "var foo = bar;", errors: 1 }
+                    ]
+                });
+            }, "Suggestion message 'Rename identifier' reported from suggestion 1 was previously reported by suggestion 0. Suggestion messages should be unique within an error.");
+        });
+
+        it("should fail if a rule produces two suggestions with the same messageId with data", () => {
+            assert.throws(() => {
+                ruleTester.run("suggestions-with-duplicate-messageids-with-data", require("../../fixtures/testers/rule-tester/suggestions").withDuplicateMessageIdsWithData, {
+                    valid: [],
+                    invalid: [
+                        { code: "var foo = bar;", errors: 1 }
+                    ]
+                });
+            }, "Suggestion message 'Rename identifier 'foo' to 'bar'' reported from suggestion 1 was previously reported by suggestion 0. Suggestion messages should be unique within an error.");
+        });
+
         it("should throw an error if a rule that doesn't have `meta.hasSuggestions` enabled produces suggestions", () => {
             assert.throws(() => {
                 ruleTester.run("suggestions-missing-hasSuggestions-property", require("../../fixtures/testers/rule-tester/suggestions").withoutHasSuggestionsProperty, {
diff --git a/tests/lib/rule-tester/rule-tester.js b/tests/lib/rule-tester/rule-tester.js
index 23a748bc536..5af50dd7dea 100644
--- a/tests/lib/rule-tester/rule-tester.js
+++ b/tests/lib/rule-tester/rule-tester.js
@@ -2187,6 +2187,39 @@ describe("RuleTester", () => {
             }, /Invalid suggestion property name 'outpt'/u);
         });
 
+        it("should fail if a rule produces two suggestions with the same description", () => {
+            assert.throws(() => {
+                ruleTester.run("suggestions-with-duplicate-descriptions", require("../../fixtures/testers/rule-tester/suggestions").withDuplicateDescriptions, {
+                    valid: [],
+                    invalid: [
+                        { code: "var foo = bar;", errors: 1 }
+                    ]
+                });
+            }, "Suggestion message 'Rename 'foo' to 'bar'' reported from suggestion 1 was previously reported by suggestion 0. Suggestion messages should be unique within an error.");
+        });
+
+        it("should fail if a rule produces two suggestions with the same messageId without data", () => {
+            assert.throws(() => {
+                ruleTester.run("suggestions-with-duplicate-messageids-no-data", require("../../fixtures/testers/rule-tester/suggestions").withDuplicateMessageIdsNoData, {
+                    valid: [],
+                    invalid: [
+                        { code: "var foo = bar;", errors: 1 }
+                    ]
+                });
+            }, "Suggestion message 'Rename identifier' reported from suggestion 1 was previously reported by suggestion 0. Suggestion messages should be unique within an error.");
+        });
+
+        it("should fail if a rule produces two suggestions with the same messageId with data", () => {
+            assert.throws(() => {
+                ruleTester.run("suggestions-with-duplicate-messageids-with-data", require("../../fixtures/testers/rule-tester/suggestions").withDuplicateMessageIdsWithData, {
+                    valid: [],
+                    invalid: [
+                        { code: "var foo = bar;", errors: 1 }
+                    ]
+                });
+            }, "Suggestion message 'Rename identifier 'foo' to 'bar'' reported from suggestion 1 was previously reported by suggestion 0. Suggestion messages should be unique within an error.");
+        });
+
         it("should throw an error if a rule that doesn't have `meta.hasSuggestions` enabled produces suggestions", () => {
             assert.throws(() => {
                 ruleTester.run("suggestions-missing-hasSuggestions-property", require("../../fixtures/testers/rule-tester/suggestions").withoutHasSuggestionsProperty, {