diff --git a/tfhe/src/integer/server_key/radix/add.rs b/tfhe/src/integer/server_key/radix/add.rs
index adddde58db..15efc98037 100644
--- a/tfhe/src/integer/server_key/radix/add.rs
+++ b/tfhe/src/integer/server_key/radix/add.rs
@@ -109,10 +109,19 @@ impl ServerKey {
     where
         T: IntegerRadixCiphertext,
     {
-        for (ct_left_i, ct_right_i) in ct_left.blocks().iter().zip(ct_right.blocks().iter()) {
-            if !self.key.is_add_possible(ct_left_i, ct_right_i) {
+        // Assumes message_modulus and carry_modulus matches between pairs of block
+        let mut preceding_block_carry = 0;
+        for (left_block, right_block) in ct_left.blocks().iter().zip(ct_right.blocks().iter()) {
+            let degree_after_add = left_block.degree.0 + right_block.degree.0;
+
+            // Also need to take into account preceding_carry
+            if (degree_after_add + preceding_block_carry)
+                >= (left_block.message_modulus.0 * left_block.carry_modulus.0)
+            {
+                // We would exceed the block 'capacity'
                 return false;
             }
+            preceding_block_carry = degree_after_add / left_block.message_modulus.0;
         }
         true
     }
diff --git a/tfhe/src/integer/server_key/radix/neg.rs b/tfhe/src/integer/server_key/radix/neg.rs
index eaff27c2f4..3f5fd66404 100644
--- a/tfhe/src/integer/server_key/radix/neg.rs
+++ b/tfhe/src/integer/server_key/radix/neg.rs
@@ -1,3 +1,4 @@
+use crate::core_crypto::prelude::misc::divide_ceil;
 use crate::integer::ciphertext::IntegerRadixCiphertext;
 use crate::integer::server_key::CheckError;
 use crate::integer::server_key::CheckError::CarryFull;
@@ -100,26 +101,35 @@ impl ServerKey {
     where
         T: IntegerRadixCiphertext,
     {
-        for i in 0..ctxt.blocks().len() {
+        let mut preceding_block_carry = 0;
+        let mut preceding_scaled_z = 0;
+        for block in ctxt.blocks().iter() {
+            let msg_mod = block.message_modulus.0;
+            let carry_mod = block.carry_modulus.0;
+            let total_modulus = msg_mod * carry_mod;
+
             // z = ceil( degree / 2^p ) x 2^p
-            let msg_mod = self.key.message_modulus.0;
-            let mut z = (ctxt.blocks()[i].degree.0 + msg_mod - 1) / msg_mod;
+            let mut z = divide_ceil(block.degree.0, msg_mod);
             z = z.wrapping_mul(msg_mod);
+            // In the actual operation, preceding_scaled_z is added to the ciphertext
+            // before doing lwe_ciphertext_opposite:
+            // i.e the code does -(ciphertext + preceding_scaled_z) + z
+            // here we do -ciphertext -preceding_scaled_z + z
+            // which is easier to express degree
+            let block_degree_after_negation = z - preceding_scaled_z;
 
-            // z will be the new degree of ctxt.blocks[i]
-            if z > self.key.max_degree.0 {
+            if block_degree_after_negation >= (total_modulus) {
                 return false;
             }
 
-            let z_b = z / msg_mod;
-
-            if i < ctxt.blocks().len() - 1
-                && !self
-                    .key
-                    .is_scalar_add_possible(&ctxt.blocks()[i + 1], z_b as u8)
-            {
+            // We want to be able to the negated block and the carry from preceding negated
+            // block to make sure carry propagation would be correct.
+            if (block_degree_after_negation + preceding_block_carry) >= (total_modulus) {
                 return false;
             }
+
+            preceding_block_carry = block_degree_after_negation / msg_mod;
+            preceding_scaled_z = z / msg_mod;
         }
         true
     }
diff --git a/tfhe/src/integer/server_key/radix/sub.rs b/tfhe/src/integer/server_key/radix/sub.rs
index 21cfe8e5be..78eed38194 100644
--- a/tfhe/src/integer/server_key/radix/sub.rs
+++ b/tfhe/src/integer/server_key/radix/sub.rs
@@ -1,3 +1,4 @@
+use crate::core_crypto::algorithms::misc::divide_ceil;
 use crate::integer::ciphertext::IntegerRadixCiphertext;
 use crate::integer::server_key::CheckError;
 use crate::integer::server_key::CheckError::CarryFull;
@@ -110,10 +111,39 @@ impl ServerKey {
     where
         T: IntegerRadixCiphertext,
     {
-        for (ct_left_i, ct_right_i) in ctxt_left.blocks().iter().zip(ctxt_right.blocks().iter()) {
-            if !self.key.is_sub_possible(ct_left_i, ct_right_i) {
+        let mut preceding_block_carry = 0;
+        let mut preceding_scaled_z = 0;
+        for (left_block, right_block) in ctxt_left.blocks().iter().zip(ctxt_right.blocks().iter()) {
+            // Assumes message_modulus and carry_modulus matches between pairs of block
+            let msg_mod = left_block.message_modulus.0;
+            let carry_mod = left_block.carry_modulus.0;
+            let total_modulus = msg_mod * carry_mod;
+
+            // z = ceil( degree / 2^p ) x 2^p
+            let mut z = divide_ceil(right_block.degree.0, msg_mod);
+            z = z.wrapping_mul(msg_mod);
+            // In the actual operation, preceding_scaled_z is added to the ciphertext
+            // before doing lwe_ciphertext_opposite:
+            // i.e the code does -(ciphertext + preceding_scaled_z) + z
+            // here we do -ciphertext -preceding_scaled_z + z
+            // which is easier to express degree
+            let right_block_degree_after_negation = z - preceding_scaled_z;
+
+            if right_block_degree_after_negation >= (total_modulus) {
                 return false;
             }
+
+            let degree_after_add = left_block.degree.0 + right_block_degree_after_negation;
+
+            // We want to be able to add the the left block, the negated right block
+            // and we also want to be able to add the carry from preceding block addition
+            // to make sure carry propagation would be correct.
+            if (degree_after_add + preceding_block_carry) >= (total_modulus) {
+                return false;
+            }
+
+            preceding_block_carry = degree_after_add / msg_mod;
+            preceding_scaled_z = z / msg_mod;
         }
         true
     }