diff --git a/src/error.rs b/src/error.rs
index 58211b7..fadb562 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -121,15 +121,16 @@ impl Error {
         }
     }
 
-    pub fn is_mismatch<E, A>(&self, has_expected: E, has_actual: A) -> bool
+    pub fn is_mismatch<E, A>(&self, want_expected: E, want_actual: A) -> bool
     where
-        String: PartialEq<E> + PartialEq<A>,
+        E: AsRef<str>,
+        A: AsRef<str>,
     {
         matches!(
             self,
             Self::Mismatch { expected, actual }
-                if *expected == has_expected
-                && *actual == has_actual
+                if expected == want_expected.as_ref()
+                && actual == want_actual.as_ref()
         )
     }
 
diff --git a/src/file/checked.rs b/src/file/checked.rs
index af52130..5804afa 100644
--- a/src/file/checked.rs
+++ b/src/file/checked.rs
@@ -104,7 +104,7 @@ impl FileTrait for Checked {
         super::check_hash(
             &self.path,
             self.size,
-            self.hash.as_ref().map(String::as_str),
+            self.hash.as_deref(),
             on_progress,
         )
     }
diff --git a/src/file/mod.rs b/src/file/mod.rs
index be26361..06a2177 100644
--- a/src/file/mod.rs
+++ b/src/file/mod.rs
@@ -16,7 +16,7 @@ pub use uploading::Uploading;
 const HASH_CHUNK_SIZE: usize = 4 * 1024 * 1024;
 
 /// compute hash for a file given its path.
-/// Hash function: BLAKE2b, 512 bit
+/// Hash function: `BLAKE2b`, 512 bit
 ///
 /// # Params
 ///
diff --git a/src/file/uploading.rs b/src/file/uploading.rs
index 9b76419..2050475 100644
--- a/src/file/uploading.rs
+++ b/src/file/uploading.rs
@@ -107,7 +107,7 @@ impl FileTrait for Uploading {
         super::check_hash(
             &self.path,
             self.size,
-            self.hash.as_ref().map(String::as_str),
+            self.hash.as_deref(),
             on_progress,
         )
     }