diff --git a/py360convert/c2e.py b/py360convert/c2e.py
index 571cb6d..f5a5612 100644
--- a/py360convert/c2e.py
+++ b/py360convert/c2e.py
@@ -116,7 +116,7 @@ def c2e(
             squeeze = False
         cube_faces = cube_dice2list(cubemap)
     else:
-        raise ValueError('Unknown cube_format "{cube_format}".')
+        raise ValueError(f'Unknown cube_format "{cube_format}".')
 
     cube_faces = np.stack(cube_faces)
 
diff --git a/py360convert/utils.py b/py360convert/utils.py
index e8451fb..7a8d9ff 100644
--- a/py360convert/utils.py
+++ b/py360convert/utils.py
@@ -548,9 +548,9 @@ def __call__(self, cube_faces: NDArray[DType]) -> NDArray[DType]:
         """
         h, w = cube_faces.shape[-2:]
         if h != self._h:
-            raise ValueError("Input height {h} doesn't match expected height {self._h}.")
+            raise ValueError(f"Input height {h} doesn't match expected height {self._h}.")
         if w != self._w:
-            raise ValueError("Input width {w} doesn't match expected height {self._w}.")
+            raise ValueError(f"Input width {w} doesn't match expected height {self._w}.")
 
         if cube_faces.dtype == np.float16:
             source_dtype = np.float16