diff --git a/Sources/Rules/NoGuardInTests.swift b/Sources/Rules/NoGuardInTests.swift
index 933e274c..fa8a4a81 100644
--- a/Sources/Rules/NoGuardInTests.swift
+++ b/Sources/Rules/NoGuardInTests.swift
@@ -75,6 +75,17 @@ public extension FormatRule {
 
                 guard isValidElseBlock else { continue }
 
+                // Preserve the assertion message (if any)
+                let assertionMessage: [Token] = {
+                    guard let startIndex = formatter.index(of: .startOfScope("("), after: elseBraceIndex),
+                          let endIndex = formatter.endOfScope(at: startIndex),
+                          formatter.index(after: startIndex, where: { $0.isStringDelimiter }) != nil
+                    else {
+                        return []
+                    }
+                    return [.delimiter(","), .space(" ")] + formatter.tokens[startIndex + 1 ..< endIndex]
+                }()
+
                 // Check for variable shadowing
                 let scopeStart = bodyRange.lowerBound
                 let searchRange = scopeStart ..< guardIndex
@@ -174,6 +185,7 @@ public extension FormatRule {
                             .startOfScope("("),
                         ])
                         replacementStatements.append(contentsOf: expressionTokens)
+                        replacementStatements.append(contentsOf: assertionMessage)
                         replacementStatements.append(.endOfScope(")"))
                         addedTryStatement = true
 
@@ -183,6 +195,7 @@ public extension FormatRule {
                         replacementStatements.append(.identifier(assertFunctionName))
                         replacementStatements.append(.startOfScope("("))
                         replacementStatements.append(contentsOf: conditionTokens)
+                        replacementStatements.append(contentsOf: assertionMessage)
                         replacementStatements.append(.endOfScope(")"))
 
                     case .patternMatching:
diff --git a/Tests/Rules/NoGuardInTestsTests.swift b/Tests/Rules/NoGuardInTestsTests.swift
index 949a21bb..84339bfd 100644
--- a/Tests/Rules/NoGuardInTestsTests.swift
+++ b/Tests/Rules/NoGuardInTestsTests.swift
@@ -56,7 +56,7 @@ final class NoGuardInTestsTests: XCTestCase {
 
         class TestCase: XCTestCase {
             func test_something() throws {
-                let value = try XCTUnwrap(optionalValue)
+                let value = try XCTUnwrap(optionalValue, "Expected value to be non-nil")
             }
         }
         """
@@ -264,6 +264,78 @@ final class NoGuardInTestsTests: XCTestCase {
         testFormatting(for: input, output, rule: .noGuardInTests, exclude: [.blankLinesAfterGuardStatements])
     }
 
+    func testPreserveFailMessage() {
+        let input = """
+        import XCTest
+
+        class TestCase: XCTestCase {
+            func test_something() {
+                guard let value1 = optionalValue1 else {
+                    XCTFail("Failed")
+                    return
+                }
+                guard optionalValue2 != nil else {
+                    XCTFail("Value was nil")
+                    return
+                }
+            }
+        }
+        """
+        let output = """
+        import XCTest
+
+        class TestCase: XCTestCase {
+            func test_something() throws {
+                let value1 = try XCTUnwrap(optionalValue1, "Failed")
+                XCTAssert(optionalValue2 != nil, "Value was nil")
+            }
+        }
+        """
+        testFormatting(for: input, output, rule: .noGuardInTests, exclude: [.blankLinesAfterGuardStatements])
+    }
+
+    func testPreserveFailMessageWithInterpolations() {
+        let input = """
+        import XCTest
+
+        class TestCase: XCTestCase {
+            func test_something() {
+                guard optionalValue2 == nil else {
+                    XCTFail("Value was \\(String(describing: optionalValue2))")
+                    return
+                }
+            }
+        }
+        """
+        let output = """
+        import XCTest
+
+        class TestCase: XCTestCase {
+            func test_something() {
+                XCTAssert(optionalValue2 == nil, "Value was \\(String(describing: optionalValue2))")
+            }
+        }
+        """
+        testFormatting(for: input, output, rule: .noGuardInTests, exclude: [.blankLinesAfterGuardStatements])
+    }
+
+    func testNoMangleNontrivialGuardBody() {
+        let input = """
+        import XCTest
+
+        class TestCase: XCTestCase {
+            func test_something() {
+                guard optionalValue2 == nil else {
+                    let value = optionalValue2 ?? ""
+                    XCTFail("Value was \\(value)")
+                    return
+                }
+            }
+        }
+        """
+        testFormatting(for: input, rule: .noGuardInTests, exclude: [.blankLinesAfterGuardStatements])
+    }
+
     func testReplaceGuardWithMultipleConditionsXCTest() {
         let input = """
         import XCTest
@@ -819,7 +891,7 @@ final class NoGuardInTestsTests: XCTestCase {
         struct SomeTests {
             @Test
             func something() throws {
-                let value = try #require(optionalValue)
+                let value = try #require(optionalValue, "Expected value to be non-nil")
             }
         }
         """