diff --git a/lib/include/srslte/phy/fec/ldpc/ldpc_rm.h b/lib/include/srslte/phy/fec/ldpc/ldpc_rm.h
index 2c087f3b6..2ccf51cc6 100644
--- a/lib/include/srslte/phy/fec/ldpc/ldpc_rm.h
+++ b/lib/include/srslte/phy/fec/ldpc/ldpc_rm.h
@@ -97,7 +97,8 @@ SRSLTE_API int srslte_ldpc_rm_rx_init_f(srslte_ldpc_rm_t* q);
  * \param[in] input      The LLRs obtained from the channel samples that correspond to
  *                       the codeword to be first, rate-dematched and then decoded.
  * \param[out] output    The rate-dematched codeword resulting from the rate-dematching
- *                       operation.
+ *                       operation. Shall be either initialized to all zeros or to the
+ *                       result of previous redundancy versions is available.
  * \param[in] E          Rate-matched codeword length.
  * \param[in] F          Number of filler bits.
  * \param[in] bg;        Current base graph.
@@ -131,6 +132,9 @@ SRSLTE_API int srslte_ldpc_rm_rx_init_s(srslte_ldpc_rm_t* q);
  *                        instance) that carries out the rate matching.
  * \param[in] input       The LLRs obtained from the channel samples that correspond to
  *                        the codeword to be first, rate-dematched and then decoded.
+ * \param[out] output    The rate-dematched codeword resulting from the rate-dematching
+ *                       operation. Shall be either initialized to all zeros or to the
+ *                       result of previous redundancy versions is available.
  * \param[in] E           Rate-matched codeword length.
  * \param[in] F           Number of filler bits.
  * \param[in] bg;         Current base graph.
@@ -165,8 +169,9 @@ SRSLTE_API int srslte_ldpc_rm_rx_init_c(srslte_ldpc_rm_t* q);
  *                        instance) that carries out the rate matching.
  * \param[in] input       The LLRs obtained from the channel samples that correspond to
  *                        the codeword to be first, rate-dematched and then decoded.
- * \param[out] output     The rate-dematched codeword resulting from the rate-dematching
- *                        operation.
+ * \param[out] output    The rate-dematched codeword resulting from the rate-dematching
+ *                       operation. Shall be either initialized to all zeros or to the
+ *                       result of previous redundancy versions is available.
  * \param[in] E           Rate-matched codeword length.
  * \param[in] F           Number of filler bits.
  * \param[in] bg;         Current base graph.
diff --git a/lib/src/phy/fec/ldpc/ldpc_rm.c b/lib/src/phy/fec/ldpc/ldpc_rm.c
index f2faf3daf..b5e34be6d 100644
--- a/lib/src/phy/fec/ldpc/ldpc_rm.c
+++ b/lib/src/phy/fec/ldpc/ldpc_rm.c
@@ -191,11 +191,12 @@ static void bit_selection_rm_tx(const uint8_t* input,
  * The output has the codeword length N. It inserts filler bits as INFINITY symbols
  * (to indicate very reliable 0 bit), and set to 0 (completely unknown bit) all
  * missing symbol. Repeated symbols are added.
+ * The input memory *output shall be either initialized to all zeros or to the
+ * result of previous redundancy versions is available.
  */
 static void bit_selection_rm_rx(const float*   input,
                                 const uint32_t in_len,
                                 float*         output,
-                                const uint32_t out_len,
                                 uint32_t*      indices,
                                 const uint32_t ini_exclude,
                                 const uint32_t end_exclude,
@@ -203,7 +204,6 @@ static void bit_selection_rm_rx(const float*   input,
                                 const uint32_t Ncb)
 {
   uint32_t E = in_len;
-  uint32_t N = out_len;
 
   uint32_t k    = 0;
   uint32_t j    = 0;
@@ -217,9 +217,6 @@ static void bit_selection_rm_rx(const float*   input,
     j = j + 1;
   } // while
 
-  // Initializes the data_decoded_vector to all zeros
-  bzero(output, N * sizeof(float));
-
   // set filler bits to INFINITY
   for (uint32_t i = ini_exclude; i < end_exclude; i++) {
     output[i] = INFINITY;
@@ -236,11 +233,12 @@ static void bit_selection_rm_rx(const float*   input,
  * The output has the codeword length N. It inserts filler bits as INFINITY symbols
  * (to indicate very reliable 0 bit), and set to 0 (completely unknown bit) all
  * missing symbol. Repeated symbols are added.
+ * The input memory *output shall be either initialized to all zeros or to the
+ * result of previous redundancy versions is available.
  */
 static void bit_selection_rm_rx_s(const int16_t* input,
                                   const uint32_t in_len,
                                   int16_t*       output,
-                                  const uint32_t out_len,
                                   uint32_t*      indices,
                                   const uint32_t ini_exclude,
                                   const uint32_t end_exclude,
@@ -248,7 +246,6 @@ static void bit_selection_rm_rx_s(const int16_t* input,
                                   const uint32_t Ncb)
 {
   uint32_t E = in_len;
-  uint32_t N = out_len;
 
   uint32_t k    = 0;
   uint32_t j    = 0;
@@ -262,9 +259,6 @@ static void bit_selection_rm_rx_s(const int16_t* input,
     j = j + 1;
   } // while
 
-  // Initializes the data_decoded_vector to all zeros
-  bzero(output, N * sizeof(int16_t));
-
   // set filler bits to INFINITY
   const long infinity16 = (1U << 15U) - 1; // Max positive value in 16-bit representation
   for (uint32_t i = ini_exclude; i < end_exclude; i++) {
@@ -293,11 +287,12 @@ static void bit_selection_rm_rx_s(const int16_t* input,
  * The output has the codeword length N. It inserts filler bits as INFINITY symbols
  * (to indicate very reliable 0 bit), and set to 0 (completely unknown bit) all
  * missing symbol. Repeated symbols are added.
+ * The input memory *output shall be either initialized to all zeros or to the
+ * result of previous redundancy versions is available.
  */
 static void bit_selection_rm_rx_c(const int8_t*  input,
                                   const uint32_t in_len,
                                   int8_t*        output,
-                                  const uint32_t out_len,
                                   uint32_t*      indices,
                                   const uint32_t ini_exclude,
                                   const uint32_t end_exclude,
@@ -305,7 +300,6 @@ static void bit_selection_rm_rx_c(const int8_t*  input,
                                   const uint32_t Ncb)
 {
   uint32_t E = in_len;
-  uint32_t N = out_len;
 
   uint32_t k    = 0;
   uint32_t j    = 0;
@@ -319,9 +313,6 @@ static void bit_selection_rm_rx_c(const int8_t*  input,
     j = j + 1;
   } // while
 
-  // Initializes the data_decoded_vector to all zeros
-  bzero(output, N * sizeof(int8_t));
-
   // set filler bits to INFINITY
   const long infinity8 = (1U << 7U) - 1; // Max positive value in 8-bit representation
   for (uint32_t i = ini_exclude; i < end_exclude; i++) {
@@ -637,10 +628,10 @@ int srslte_ldpc_rm_rx_f(srslte_ldpc_rm_t*        q,
   uint32_t         ini_exclude   = end_exclude - q->F;
 
   if (q->mod_order == 1) { // interleaver can be skipped
-    bit_selection_rm_rx(input, q->E, output, q->N, indices, ini_exclude, end_exclude, q->k0, q->Ncb);
+    bit_selection_rm_rx(input, q->E, output, indices, ini_exclude, end_exclude, q->k0, q->Ncb);
   } else {
     bit_interleaver_rm_rx(input, tmp_rm_symbol, q->E, q->mod_order);
-    bit_selection_rm_rx(tmp_rm_symbol, q->E, output, q->N, indices, ini_exclude, end_exclude, q->k0, q->Ncb);
+    bit_selection_rm_rx(tmp_rm_symbol, q->E, output, indices, ini_exclude, end_exclude, q->k0, q->Ncb);
   }
   return 0;
 }
@@ -669,10 +660,10 @@ int srslte_ldpc_rm_rx_s(srslte_ldpc_rm_t*        q,
   uint32_t         ini_exclude   = end_exclude - q->F;
 
   if (q->mod_order == 1) { // interleaver can be skipped
-    bit_selection_rm_rx_s(input, q->E, output, q->N, indices, ini_exclude, end_exclude, q->k0, q->Ncb);
+    bit_selection_rm_rx_s(input, q->E, output, indices, ini_exclude, end_exclude, q->k0, q->Ncb);
   } else {
     bit_interleaver_rm_rx_s(input, tmp_rm_symbol, q->E, q->mod_order);
-    bit_selection_rm_rx_s(tmp_rm_symbol, q->E, output, q->N, indices, ini_exclude, end_exclude, q->k0, q->Ncb);
+    bit_selection_rm_rx_s(tmp_rm_symbol, q->E, output, indices, ini_exclude, end_exclude, q->k0, q->Ncb);
   }
 
   return 0;
@@ -702,10 +693,10 @@ int srslte_ldpc_rm_rx_c(srslte_ldpc_rm_t*        q,
   uint32_t         ini_exclude   = end_exclude - q->F;
 
   if (q->mod_order == 1) { // interleaver can be skipped
-    bit_selection_rm_rx_c(input, q->E, output, q->N, indices, ini_exclude, end_exclude, q->k0, q->Ncb);
+    bit_selection_rm_rx_c(input, q->E, output, indices, ini_exclude, end_exclude, q->k0, q->Ncb);
   } else {
     bit_interleaver_rm_rx_c(input, tmp_rm_symbol, q->E, q->mod_order);
-    bit_selection_rm_rx_c(tmp_rm_symbol, q->E, output, q->N, indices, ini_exclude, end_exclude, q->k0, q->Ncb);
+    bit_selection_rm_rx_c(tmp_rm_symbol, q->E, output, indices, ini_exclude, end_exclude, q->k0, q->Ncb);
   }
 
   return 0;
diff --git a/lib/src/phy/fec/ldpc/test/ldpc_rm_chain_test.c b/lib/src/phy/fec/ldpc/test/ldpc_rm_chain_test.c
index 7179e226d..219f9ca2b 100644
--- a/lib/src/phy/fec/ldpc/test/ldpc_rm_chain_test.c
+++ b/lib/src/phy/fec/ldpc/test/ldpc_rm_chain_test.c
@@ -407,6 +407,14 @@ int main(int argc, char** argv)
       }
     }
 
+    // HARQ procedure. Use previous previous rate-matched outputs if available from the previous redundancy versions,
+    // otherwise initialize to zeros.
+    for (i = 0; i < batch_size; i++) {
+      bzero(symbols + i * finalN, finalN * sizeof(float));
+      bzero(symbols_s + i * finalN, finalN * sizeof(int16_t));
+      bzero(symbols_c + i * finalN, finalN * sizeof(int8_t));
+    }
+
     for (i = 0; i < batch_size; i++) {
       if (srslte_ldpc_rm_rx_f(&rm_rx,
                               rm_symbols + i * rm_length,
diff --git a/lib/src/phy/fec/ldpc/test/ldpc_rm_test.c b/lib/src/phy/fec/ldpc/test/ldpc_rm_test.c
index 6b0d053c2..319d5c194 100644
--- a/lib/src/phy/fec/ldpc/test/ldpc_rm_test.c
+++ b/lib/src/phy/fec/ldpc/test/ldpc_rm_test.c
@@ -250,6 +250,12 @@ int main(int argc, char** argv)
       rm_symbols_c[r * E + i] = rm_codewords[r * E + i] ? -1 : 1;
     }
 
+    // HARQ procedure. Use previous previous rate-matched outputs if available from the previous redundancy versions,
+    // otherwise initialize to zeros.
+    bzero(unrm_symbols + r * N, N * sizeof(float));
+    bzero(unrm_symbols_s + r * N, N * sizeof(int16_t));
+    bzero(unrm_symbols_c + r * N, N * sizeof(int8_t));
+
     if (srslte_ldpc_rm_rx_f(
             &rm_rx, rm_symbols + r * E, unrm_symbols + r * N, E, F, base_graph, lift_size, rv, mod_type, Nref)) {
       exit(-1);