diff --git a/src/lib.rs b/src/lib.rs
index 29115c9..efc91d4 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -621,10 +621,7 @@ pub mod fmt {

 /// Unicode string slice manipulation for quantities.
 pub mod str {
-    use core::fmt::{self, Display, Formatter};
-
-    #[cfg(feature = "std")]
-    use std::error::Error;
+    use crate::lib::fmt::{self, Display, Formatter};

     /// Represents an error encountered while parsing a string into a `Quantity`.
     #[allow(missing_copy_implementations)]
@@ -654,11 +651,11 @@ pub mod str {
             match *self {
                 NoSeparator => write!(f, "no space between quantity and units"),
                 ValueParseError => write!(f, "error parsing unit quantity"),
-                UnknownUnit => write!(f, "unrecognized parsing unit of measure"),
+                UnknownUnit => write!(f, "unrecognized unit of measure"),
             }
         }
     }

     #[cfg(feature = "std")]
-    impl Error for ParseQuantityError {}
+    impl crate::lib::error::Error for ParseQuantityError {}
 }