diff --git a/utils/grid/lib.rs b/utils/grid/lib.rs
index daed417..f2fa866 100644
--- a/utils/grid/lib.rs
+++ b/utils/grid/lib.rs
@@ -452,7 +452,7 @@ impl<T: Clone + Eq + PartialEq + Debug> Grid<T> {
     }
 
     /// Return an iterator over the 8 neighbours of c. The iterator skips neighbouring positions outside of the grid.
-    pub fn adjacent_iter<C: AsCoord2d + Copy>(&self, c: &C) -> OffsetsIter<T> {
+    pub fn adjacent_iter<'a, C: AsCoord2d + Copy>(&'a self, c: &'a C) -> OffsetsIter<'a, T> {
         OffsetsIter {
             grid: self,
             origin: c.to_coord(),
@@ -462,7 +462,7 @@ impl<T: Clone + Eq + PartialEq + Debug> Grid<T> {
     }
 
     /// Return an iterator over the 4 cardinal neighbours of c. The iterator skips neighbouring positions outside of the grid.
-    pub fn cardinal_iter<C: AsCoord2d + Copy>(&self, c: &C) -> OffsetsIter<T> {
+    pub fn cardinal_iter<'a, C: AsCoord2d + Copy>(&'a self, c: &'a C) -> OffsetsIter<'a, T> {
         OffsetsIter {
             grid: self,
             origin: c.to_coord(),