diff --git a/src/cuda_backend.rs b/src/cuda_backend.rs
index d12db972..7858e542 100644
--- a/src/cuda_backend.rs
+++ b/src/cuda_backend.rs
@@ -1,4 +1,4 @@
-use crate::{CpuStorage, DType, Result, Shape};
+use crate::{CpuStorage, DType, Error, Result, Shape};
 use cudarc::driver::{CudaSlice, LaunchAsync, LaunchConfig};
 
 pub type CudaError = cudarc::driver::DriverError;
@@ -92,7 +92,7 @@ impl CudaStorage {
         match self {
             Self::F32(arg) => {
                 if !shape.is_contiguous(stride) {
-                    todo!("affine is only implemented for the contiguous case")
+                    return Err(Error::RequiresContiguous { op: "affine" });
                 }
                 let dev = arg.device();
                 let module_name = "affine_f32";
diff --git a/src/dummy_cuda_backend.rs b/src/dummy_cuda_backend.rs
index f555327f..85b5f598 100644
--- a/src/dummy_cuda_backend.rs
+++ b/src/dummy_cuda_backend.rs
@@ -1,5 +1,5 @@
 #![allow(dead_code)]
-use crate::{CpuStorage, DType, Result, Shape};
+use crate::{CpuStorage, DType, Error, Result, Shape};
 
 pub type CudaError = std::io::Error;
 
@@ -14,7 +14,7 @@ macro_rules! fail {
 
 impl CudaDevice {
     pub(crate) fn new(_: usize) -> Result<Self> {
-        fail!()
+        Err(Error::NotCompiledWithCudaSupport)
     }
 
     pub(crate) fn ordinal(&self) -> usize {
@@ -22,11 +22,11 @@ impl CudaDevice {
     }
 
     pub(crate) fn zeros_impl(&self, _shape: &Shape, _dtype: DType) -> Result<CudaStorage> {
-        fail!()
+        Err(Error::NotCompiledWithCudaSupport)
     }
 
     pub(crate) fn cuda_from_cpu_storage(&self, _: &CpuStorage) -> Result<CudaStorage> {
-        fail!()
+        Err(Error::NotCompiledWithCudaSupport)
     }
 }
 
@@ -43,10 +43,10 @@ impl CudaStorage {
     }
 
     pub(crate) fn to_cpu_storage(&self) -> Result<CpuStorage> {
-        fail!()
+        Err(Error::NotCompiledWithCudaSupport)
     }
 
     pub(crate) fn affine_impl(&self, _: &Shape, _: &[usize], _: f64, _: f64) -> Result<Self> {
-        fail!()
+        Err(Error::NotCompiledWithCudaSupport)
     }
 }
diff --git a/src/error.rs b/src/error.rs
index 3f142960..27201cb4 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -6,6 +6,12 @@ pub enum Error {
     #[error("unexpected dtype, expected: {expected:?}, got: {got:?}")]
     UnexpectedDType { expected: DType, got: DType },
 
+    #[error("{op} only supports contiguous tensors")]
+    RequiresContiguous { op: &'static str },
+
+    #[error("the candle crate has not been built with cuda support")]
+    NotCompiledWithCudaSupport,
+
     #[error("shape mismatch in {op}, lhs: {lhs:?}, rhs: {rhs:?}")]
     ShapeMismatchBinaryOp {
         lhs: Shape,