diff --git a/src/util/pattern.rs b/src/util/pattern.rs
index a857bff..7ea35d6 100644
--- a/src/util/pattern.rs
+++ b/src/util/pattern.rs
@@ -8,11 +8,12 @@ type ParseError = Box<dyn std::error::Error>;
 
 trait Pattern<'a> {
     pub fn execute(&self, values: &'a mut [RawColor]);
-    pub fn parse(args: Vec<String>) -> Result<Self, ParseError>;
+    pub fn parse(args: Vec<String>) -> Result<Self, ParseError> where Self: Sized;
 }
 
 impl<'a> TryFrom<Vec<String>> for Box<dyn Pattern<'a>> {
-    fn try_from(s: Vec<String>) -> Result<Self, ParseError> {
+    type Error = ParseError;
+    fn try_from(s: Vec<String>) -> Result<Self, Error> {
         match s[0].as_str() {
             "unit" => Unit::parse(s),
             "val" => Value::parse(s),
@@ -96,4 +97,4 @@ impl<'a> Pattern<'a> for Value {
 pub fn parse_line(v: Vec<String>) -> Result<Box<dyn Pattern<'static>>, ParseError> {
     let res: Result<Box<dyn Pattern>, ParseError> = v.try_into();
     res
-}
\ No newline at end of file
+}