diff --git a/src/error.rs b/src/error.rs
index 9ed3ab1..1b8618c 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -18,7 +18,7 @@ pub enum ValidateError {
     ExtrapolateSelection(String),
     #[error("supplied grid coordinates cannot be empty: dim {0}")]
     EmptyGrid(usize),
-    #[error("supplied coordinates must be sorted and non-repeating: dim {0}")]
+    #[error("supplied coordinates must be monotonically increasing: dim {0}")]
     Monotonicity(usize),
     #[error("supplied grid and values are not compatible shapes: dim {0}")]
     IncompatibleShapes(usize),