diff --git a/src/mako/lib/mbuild.mako b/src/mako/lib/mbuild.mako
index ed6f8d134ef..1aabbc81260 100644
--- a/src/mako/lib/mbuild.mako
+++ b/src/mako/lib/mbuild.mako
@@ -361,6 +361,7 @@ match result {
     Result::HttpError(err) => println!("HTTPERROR: {:?}", err),
     Result::MissingAPIKey => println!("Auth: Missing API Key - used if there are no scopes"),
     Result::MissingToken => println!("OAuth2: Missing Token"),
+    Result::UploadSizeLimitExceeded(size, max_size) => println!("Upload size too big: {} of {}", size, max_size),
     Result::Failure(_) => println!("General Failure (hyper::client::Response doesn't print)"),
     Result::FieldClash(clashed_field) => println!("You added custom parameter which is part of builder: {:?}", clashed_field),
     Result::JsonDecodeError(err) => println!("Couldn't understand server reply - maybe API needs update: {:?}", err),
@@ -440,7 +441,10 @@ match result {
     all_required_param_name = set(p.name for p in params if is_required_property(p))
     MULTI_SLASH = 'multi-slash-prefix'
     URL_ENCODE = 'url-encode'
-    READER_SEEK = "let size = reader.seek(io::SeekFrom::End(0)).unwrap();\nreader.seek(io::SeekFrom::Start(0)).unwrap();"
+
+    max_size = simple_media_param.max_size
+    READER_SEEK = "let size = reader.seek(io::SeekFrom::End(0)).unwrap();\nreader.seek(io::SeekFrom::Start(0)).unwrap();\n"
+    READER_SEEK += "if size > %i {\n\treturn Result::UploadSizeLimitExceeded(size, %i)\n}" % (max_size, max_size)
 
     special_cases = set()
     for possible_url in possible_urls:
diff --git a/src/rust/cmn.rs b/src/rust/cmn.rs
index 3152b0c7cfa..9668f7709c7 100644
--- a/src/rust/cmn.rs
+++ b/src/rust/cmn.rs
@@ -195,6 +195,10 @@ pub enum Result<T = ()> {
     /// The http connection failed
     HttpError(hyper::HttpError),
 
+    /// An attempt was made to upload a resource with size stored in field `.0`
+    /// even though the maximum upload size is what is stored in field `.1`.
+    UploadSizeLimitExceeded(u64, u64),
+
     /// We needed an API key for authentication, but didn't obtain one.
     /// Neither through the authenticator, nor through the Delegate.
     MissingAPIKey,