diff --git a/exercises/rna-transcription/Sources/RnaTranscriptionExample.swift b/exercises/rna-transcription/Sources/RnaTranscriptionExample.swift
index 78b88018f..3968390b0 100644
--- a/exercises/rna-transcription/Sources/RnaTranscriptionExample.swift
+++ b/exercises/rna-transcription/Sources/RnaTranscriptionExample.swift
@@ -1,5 +1,5 @@
 enum TranscriptionError: Error {
-    case invalidNucleotide
+    case invalidNucleotide(String)
 }
 
 struct Nucleotide {
@@ -19,7 +19,7 @@ struct Nucleotide {
         var tempText = ""
         for each in self.value.characters {
             if dict[each] == nil {
-                throw TranscriptionError.invalidNucleotide
+                throw TranscriptionError.invalidNucleotide("\(each) is not a valid Nucleotide")
             }
             tempText += dict[each] ?? ""
         }
diff --git a/exercises/rna-transcription/Tests/RnaTranscriptionTests/RnaTranscriptionTests.swift b/exercises/rna-transcription/Tests/RnaTranscriptionTests/RnaTranscriptionTests.swift
index 567927bc8..0e3d7fba7 100644
--- a/exercises/rna-transcription/Tests/RnaTranscriptionTests/RnaTranscriptionTests.swift
+++ b/exercises/rna-transcription/Tests/RnaTranscriptionTests/RnaTranscriptionTests.swift
@@ -23,30 +23,33 @@ class RnaTranscriptionTests: XCTestCase {
     }
 
     func testInvalidRnaComplementOfUracil() {
-        XCTAssertThrowsError(try Nucleotide("U").complementOfDNA())
-
-        // Uncomment to see more specific error handling
-//        XCTAssertThrowsError(try Nucleotide("U").complementOfDNA(), "This didn't work") { (error) in
-//            XCTAssertEqual(error as? RnaTranscription.TranscriptionError, RnaTranscription.TranscriptionError.invalidNucleotide)
-//        }
+        XCTAssertThrowsError(try Nucleotide("U").complementOfDNA()) { (error) in
+            if case let RnaTranscription.TranscriptionError.invalidNucleotide(message) = error {
+                XCTAssertTrue(message == "U is not a valid Nucleotide")
+            } else {
+                XCTFail("Expected error not thrown")
+            }
+        }
     }
 
     func testInvalidRnaComplementOfXXX() {
-        XCTAssertThrowsError(try Nucleotide("XXX").complementOfDNA())
-
-        // Uncomment to see more specific error handling
-//        XCTAssertThrowsError(try Nucleotide("XXX").complementOfDNA(), "This didn't work") { (error) in
-//            XCTAssertEqual(error as? RnaTranscription.TranscriptionError, RnaTranscription.TranscriptionError.invalidNucleotide)
-//        }
+        XCTAssertThrowsError(try Nucleotide("XXX").complementOfDNA()) { (error) in
+            if case let RnaTranscription.TranscriptionError.invalidNucleotide(message) = error {
+                XCTAssertTrue(message == "X is not a valid Nucleotide")
+            } else {
+                XCTFail("Expected error not thrown")
+            }
+        }
     }
 
     func testInvalidRnaComplementOfACGTXXXCTTAA() {
-        XCTAssertThrowsError(try Nucleotide("ACGTXXXCTTAA").complementOfDNA())
-
-        // Uncomment to see more specific error handling
-//        XCTAssertThrowsError(try Nucleotide("ACGTXXXCTTAA").complementOfDNA(), "This didn't work") { (error) in
-//            XCTAssertEqual(error as? RnaTranscription.TranscriptionError, RnaTranscription.TranscriptionError.invalidNucleotide)
-//        }
+        XCTAssertThrowsError(try Nucleotide("ACGTXXXCTTAA").complementOfDNA()) { error in
+            if case let RnaTranscription.TranscriptionError.invalidNucleotide(message) = error {
+                XCTAssertTrue(message == "X is not a valid Nucleotide")
+            } else {
+                XCTFail("Expected error not thrown")
+            }
+        }
     }
 
     static var allTests: [(String, (RnaTranscriptionTests) -> () throws -> Void)] {