diff --git a/stdlib/public/core/UTF8EncodingError.swift b/stdlib/public/core/UTF8EncodingError.swift
index 9956b5ec35750..aeaaee5f50866 100644
--- a/stdlib/public/core/UTF8EncodingError.swift
+++ b/stdlib/public/core/UTF8EncodingError.swift
@@ -256,6 +256,7 @@ extension UTF8 {
           errors.append(adjustedErr)
         }
       }
+      fatalError()
     }
   }
 }