diff --git a/src/error.rs b/src/error.rs
index fadb562..9199f38 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -62,6 +62,8 @@ pub enum Error {
     Unknown(String),
 }
 
+pub type Result<T> = std::result::Result<T, Error>;
+
 // a helper to generate all the `From<T> for Error` impls
 macro_rules! impl_error_from {
     // $typ: the source type
@@ -114,11 +116,11 @@ impl Error {
         Self::Response(into_string(e))
     }
 
-    pub fn mismatch(expected: impl ToString, actual: impl ToString) -> Self {
-        Self::Mismatch {
+    pub fn mismatch<T>(expected: impl ToString, actual: impl ToString) -> Result<T> {
+        Err(Self::Mismatch {
             expected: into_string(expected),
             actual: into_string(actual),
-        }
+        })
     }
 
     pub fn is_mismatch<E, A>(&self, want_expected: E, want_actual: A) -> bool
@@ -152,5 +154,3 @@ impl Error {
         }
     }
 }
-
-pub type Result<T> = std::result::Result<T, Error>;
diff --git a/src/file/checked.rs b/src/file/checked.rs
index 2adf26e..a4d9c8e 100644
--- a/src/file/checked.rs
+++ b/src/file/checked.rs
@@ -68,7 +68,7 @@ impl Checked {
     /// TODO this could use an error variant like `IllegalInvocation`
     pub fn hash(&mut self, on_progress: impl FnMut(u64)) -> crate::Result<()> {
         if self.hash.is_some() {
-            return Err(crate::Error::mismatch("unhashed file", self.path.display()));
+            return crate::Error::mismatch("unhashed file", self.path.display());
         }
 
         self.hash = Some(super::compute_hash(&self.path, self.size, on_progress)?);
diff --git a/src/file/chunk.rs b/src/file/chunk.rs
index a6f0b05..129c331 100644
--- a/src/file/chunk.rs
+++ b/src/file/chunk.rs
@@ -39,7 +39,7 @@ impl<'t> Chunk<'t> {
         self.data
     }
 
-    pub(super) fn get_length(&self) -> u64 {
+    pub fn get_length(&self) -> u64 {
         let len = self.data.len();
 
         // BOOKMARK this might **panic** on platforms where `usize` has more than 64 bit.
@@ -47,10 +47,6 @@ impl<'t> Chunk<'t> {
         // Whoa! Maybe just chill?
         u64::try_from(len).unwrap_or_else(|e| panic!("usize={len} did not fit into u64: {e}"))
     }
-
-    pub fn get_behind(&self) -> u64 {
-        self.offset + self.get_length()
-    }
 }
 
 #[cfg(test)]
@@ -80,7 +76,6 @@ mod tests {
             assert_eq!(chunk.get_offset(), mock_offset);
             assert_eq!(chunk.get_data(), data);
             assert_eq!(chunk.get_length(), len);
-            assert_eq!(chunk.get_behind(), mock_offset + len);
         }
     }
 }
diff --git a/src/file/mod.rs b/src/file/mod.rs
index 246df07..8420d48 100644
--- a/src/file/mod.rs
+++ b/src/file/mod.rs
@@ -51,7 +51,7 @@ fn compute_hash(path: &Path, size: u64, mut on_progress: impl FnMut(u64)) -> cra
     }
 
     if bytes_read != size {
-        return Err(crate::Error::mismatch(size, bytes_read));
+        return crate::Error::mismatch(size, bytes_read);
     }
 
     let result = BASE64.encode(hasher.finalize());
@@ -79,7 +79,7 @@ fn check_hash(
 ) -> crate::Result<()> {
     // check if hash is None
     let Some(expected) = hash else {
-        return Err(crate::Error::mismatch("hash", path.display()));
+        return crate::Error::mismatch("hash", path.display());
     };
 
     // compute and check new hash
@@ -90,7 +90,7 @@ fn check_hash(
         Ok(())
     } else {
         warn!("hash mismatch for file {:?}", path.display());
-        Err(crate::Error::mismatch(expected, actual))
+        crate::Error::mismatch(expected, actual)
     }
 }
 
diff --git a/src/impl_ureq.rs b/src/impl_ureq.rs
index c4bacee..ed12cf2 100644
--- a/src/impl_ureq.rs
+++ b/src/impl_ureq.rs
@@ -76,7 +76,7 @@ impl sharry::Client for ureq::Agent {
 
             Ok(res.id.into())
         } else {
-            Err(crate::Error::response(format!("{res:?}")))
+            crate::Error::mismatch("success/\"Share created.\"", format_args!("{res:?}"))
         }
     }
 
@@ -168,15 +168,12 @@ impl sharry::Client for ureq::Agent {
             .map_err(crate::Error::response)?
             .parse::<u64>()
             .map_err(crate::Error::response)?;
+        let next_offset = chunk.get_offset() + chunk.get_length();
 
-        if chunk.get_behind() == res_offset {
+        if res_offset == next_offset {
             Ok(())
         } else {
-            Err(crate::Error::response(format!(
-                "Unexpected Upload-Offset: {} (expected {})",
-                res_offset,
-                chunk.get_behind()
-            )))
+            crate::Error::mismatch(format_args!("Upload-Offset {next_offset:?}"), res_offset)
         }
     }
 }
diff --git a/src/sharry/ids.rs b/src/sharry/ids.rs
index 24412e0..62e054f 100644
--- a/src/sharry/ids.rs
+++ b/src/sharry/ids.rs
@@ -103,10 +103,10 @@ impl TryFrom<String> for FileID {
 
             Ok(result)
         } else {
-            Err(crate::Error::mismatch(
+            crate::Error::mismatch(
                 "<proto>://<host>/api/v2/alias/upload/<share>/files/tus/<file>",
                 value,
-            ))
+            )
         }
     }
 }