diff --git a/backend/src/encoding.rs b/backend/src/encoding.rs
index 48501b6..73b86a3 100644
--- a/backend/src/encoding.rs
+++ b/backend/src/encoding.rs
@@ -267,7 +267,7 @@ fn decode_coeff_i64<D: AsRef<[u8]>>(a: &VecZnx<D>, col_i: usize, basek: usize, k
     let data: &[i64] = a.raw();
     let mut res: i64 = data[i];
     let rem: usize = basek - (k % basek);
-    let slice_size: usize = a.n() * a.size();
+    let slice_size: usize = a.n() * a.cols();
     (1..size).for_each(|i| {
         let x: i64 = data[i * slice_size];
         if i == size - 1 && rem != basek {
diff --git a/core/src/ggsw_ciphertext.rs b/core/src/ggsw_ciphertext.rs
index ca22faf..7215adf 100644
--- a/core/src/ggsw_ciphertext.rs
+++ b/core/src/ggsw_ciphertext.rs
@@ -142,14 +142,13 @@ impl GGSWCiphertext<Vec<u8>, FFT64> {
         tensor_key_size: usize,
         rank: usize,
     ) -> usize {
-        GGSWCiphertext::keyswitch_scratch_space(
-            module,
-            out_size,
-            in_size,
-            auto_key_size,
-            tensor_key_size,
-            rank,
-        )
+        let cols: usize = rank + 1;
+        let res: usize = module.bytes_of_vec_znx(cols, out_size);
+        let res_dft: usize = module.bytes_of_vec_znx_dft(cols, out_size);
+        let ci_dft: usize = module.bytes_of_vec_znx_dft(cols, out_size);
+        let ks_internal: usize = GGSWCiphertext::keyswitch_internal_col0_scratch_space(module, out_size, in_size, auto_key_size, rank);
+        let expand: usize = GGSWCiphertext::expand_row_scratch_space(module, out_size, tensor_key_size, rank);
+        res + ci_dft + (ks_internal | expand | res_dft)
     }
 
     pub fn automorphism_inplace_scratch_space(
@@ -288,6 +287,8 @@ where
     {
         let cols: usize = self.rank() + 1;
 
+        assert!(scratch.available() >= GGSWCiphertext::expand_row_scratch_space(module, self.size(), tsk.size(), tsk.rank()));
+
         // Example for rank 3:
         //
         // Note: M is a vector (m, Bm, B^2m, B^3m, ...), so each column is
@@ -383,7 +384,7 @@ where
             k: self.k(),
         };
 
-        let (mut ci_dft, scratch2) = scratch1.tmp_vec_znx_dft(module, cols, self.size());
+        let (mut ci_dft, scratch2) = scratch1.tmp_vec_znx_dft(module, cols, lhs.size());
 
         // Keyswitch the j-th row of the col 0
         (0..lhs.rows()).for_each(|row_i| {
@@ -467,6 +468,7 @@ where
                 self.rank(),
                 tensor_key.rank()
             );
+            assert!(scratch.available() >= GGSWCiphertext::automorphism_scratch_space(module, self.size(), lhs.size(), auto_key.size(), tensor_key.size(), self.rank()))
         };
 
         let cols: usize = self.rank() + 1;
@@ -646,6 +648,7 @@ where
         {
             assert_eq!(self.rank(), ksk.rank());
             assert_eq!(res.rank(), ksk.rank());
+            assert!(scratch.available() >= GGSWCiphertext::keyswitch_internal_col0_scratch_space(module, res.size(), self.size(), ksk.size(), ksk.rank()))
         }
 
         let (tmp_dft_in_data, scratch2) = scratch.tmp_vec_znx_dft(module, self.rank() + 1, self.size());
diff --git a/core/src/tensor_key.rs b/core/src/tensor_key.rs
index 105dace..89ce299 100644
--- a/core/src/tensor_key.rs
+++ b/core/src/tensor_key.rs
@@ -17,7 +17,7 @@ pub struct TensorKey<C, B: Backend> {
 impl TensorKey<Vec<u8>, FFT64> {
     pub fn alloc(module: &Module<FFT64>, basek: usize, k: usize, rows: usize, rank: usize) -> Self {
         let mut keys: Vec<GLWESwitchingKey<Vec<u8>, FFT64>> = Vec::new();
-        let pairs: usize = ((rank + 1) * rank) >> 1;
+        let pairs: usize = (((rank + 1) * rank) >> 1).max(1);
         (0..pairs).for_each(|_| {
             keys.push(GLWESwitchingKey::alloc(module, basek, k, rows, 1, rank));
         });