diff --git a/src/ascii.rs b/src/ascii.rs
index f513ab6..ac3cd52 100644
--- a/src/ascii.rs
+++ b/src/ascii.rs
@@ -109,6 +109,8 @@ impl<S: AsRef<str>> Hash for Ascii<S> {
         for byte in self.as_ref().bytes().map(|b| b.to_ascii_lowercase()) {
             hasher.write_u8(byte);
         }
+        // prefix-freedom
+        hasher.write_u8(0xFF);
     }
 }
 
diff --git a/src/unicode/mod.rs b/src/unicode/mod.rs
index ff5eff8..aec7b07 100644
--- a/src/unicode/mod.rs
+++ b/src/unicode/mod.rs
@@ -70,6 +70,8 @@ impl<S: AsRef<str>> Hash for Unicode<S> {
                 hasher.write_u8(b);
             }
         }
+        // prefix-freedom
+        hasher.write_u8(0xFF);
     }
 }