diff --git a/crypto_kem/frodokem1344aes/opt/matrix_aes.c b/crypto_kem/frodokem1344aes/opt/matrix_aes.c
index 58a91fba..ca461c99 100644
--- a/crypto_kem/frodokem1344aes/opt/matrix_aes.c
+++ b/crypto_kem/frodokem1344aes/opt/matrix_aes.c
@@ -110,10 +110,10 @@ int PQCLEAN_FRODOKEM1344AES_OPT_mul_add_sa_plus_e(uint16_t *out, const uint16_t
                 uint16_t sum[PARAMS_PARALLEL] = {0};
                 for (j = 0; j < PARAMS_N; j++) {                // Matrix-vector multiplication
                     uint16_t sp = s[i * PARAMS_N + j];
-                    sum[0] += sp * a_cols_t[(k + 0) * PARAMS_N + j];
-                    sum[1] += sp * a_cols_t[(k + 1) * PARAMS_N + j];
-                    sum[2] += sp * a_cols_t[(k + 2) * PARAMS_N + j];
-                    sum[3] += sp * a_cols_t[(k + 3) * PARAMS_N + j];
+                    sum[0] += (uint16_t)(sp * (uint32_t)a_cols_t[(k + 0) * PARAMS_N + j]);
+                    sum[1] += (uint16_t)(sp * (uint32_t)a_cols_t[(k + 1) * PARAMS_N + j]);
+                    sum[2] += (uint16_t)(sp * (uint32_t)a_cols_t[(k + 2) * PARAMS_N + j]);
+                    sum[3] += (uint16_t)(sp * (uint32_t)a_cols_t[(k + 3) * PARAMS_N + j]);
                 }
                 out[i * PARAMS_N + kk + k + 0] += sum[0];
                 out[i * PARAMS_N + kk + k + 2] += sum[2];
diff --git a/crypto_kem/frodokem1344shake/opt/matrix_shake.c b/crypto_kem/frodokem1344shake/opt/matrix_shake.c
index 7fab5e5f..6d037ec1 100644
--- a/crypto_kem/frodokem1344shake/opt/matrix_shake.c
+++ b/crypto_kem/frodokem1344shake/opt/matrix_shake.c
@@ -96,7 +96,7 @@ int PQCLEAN_FRODOKEM1344SHAKE_OPT_mul_add_sa_plus_e(uint16_t *out, const uint16_
             for (j = 0; j < 4; j++) {
                 uint16_t sp = s[i * PARAMS_N + kk + j];
                 for (k = 0; k < PARAMS_N; k++) {                // Matrix-vector multiplication
-                    sum[k] += sp * a_cols[(t + j) * PARAMS_N + k];
+                    sum[k] += (uint16_t)(sp * (uint32_t)a_cols[(t + j) * PARAMS_N + k]);
                 }
             }
             for (k = 0; k < PARAMS_N; k++) {
diff --git a/crypto_kem/frodokem640aes/opt/matrix_aes.c b/crypto_kem/frodokem640aes/opt/matrix_aes.c
index 2d858502..3f245fcf 100644
--- a/crypto_kem/frodokem640aes/opt/matrix_aes.c
+++ b/crypto_kem/frodokem640aes/opt/matrix_aes.c
@@ -110,10 +110,10 @@ int PQCLEAN_FRODOKEM640AES_OPT_mul_add_sa_plus_e(uint16_t *out, const uint16_t *
                 uint16_t sum[PARAMS_PARALLEL] = {0};
                 for (j = 0; j < PARAMS_N; j++) {                // Matrix-vector multiplication
                     uint16_t sp = s[i * PARAMS_N + j];
-                    sum[0] += sp * a_cols_t[(k + 0) * PARAMS_N + j];
-                    sum[1] += sp * a_cols_t[(k + 1) * PARAMS_N + j];
-                    sum[2] += sp * a_cols_t[(k + 2) * PARAMS_N + j];
-                    sum[3] += sp * a_cols_t[(k + 3) * PARAMS_N + j];
+                    sum[0] += (uint16_t)(sp * (uint32_t)a_cols_t[(k + 0) * PARAMS_N + j]);
+                    sum[1] += (uint16_t)(sp * (uint32_t)a_cols_t[(k + 1) * PARAMS_N + j]);
+                    sum[2] += (uint16_t)(sp * (uint32_t)a_cols_t[(k + 2) * PARAMS_N + j]);
+                    sum[3] += (uint16_t)(sp * (uint32_t)a_cols_t[(k + 3) * PARAMS_N + j]);
                 }
                 out[i * PARAMS_N + kk + k + 0] += sum[0];
                 out[i * PARAMS_N + kk + k + 2] += sum[2];
diff --git a/crypto_kem/frodokem640shake/opt/matrix_shake.c b/crypto_kem/frodokem640shake/opt/matrix_shake.c
index 3094f2a9..fa8a5f06 100644
--- a/crypto_kem/frodokem640shake/opt/matrix_shake.c
+++ b/crypto_kem/frodokem640shake/opt/matrix_shake.c
@@ -96,7 +96,7 @@ int PQCLEAN_FRODOKEM640SHAKE_OPT_mul_add_sa_plus_e(uint16_t *out, const uint16_t
             for (j = 0; j < 4; j++) {
                 uint16_t sp = s[i * PARAMS_N + kk + j];
                 for (k = 0; k < PARAMS_N; k++) {                // Matrix-vector multiplication
-                    sum[k] += sp * a_cols[(t + j) * PARAMS_N + k];
+                    sum[k] += (uint16_t)(sp * (uint32_t)a_cols[(t + j) * PARAMS_N + k]);
                 }
             }
             for (k = 0; k < PARAMS_N; k++) {
diff --git a/crypto_kem/frodokem976aes/opt/matrix_aes.c b/crypto_kem/frodokem976aes/opt/matrix_aes.c
index ddff99ac..8461bda0 100644
--- a/crypto_kem/frodokem976aes/opt/matrix_aes.c
+++ b/crypto_kem/frodokem976aes/opt/matrix_aes.c
@@ -110,10 +110,10 @@ int PQCLEAN_FRODOKEM976AES_OPT_mul_add_sa_plus_e(uint16_t *out, const uint16_t *
                 uint16_t sum[PARAMS_PARALLEL] = {0};
                 for (j = 0; j < PARAMS_N; j++) {                // Matrix-vector multiplication
                     uint16_t sp = s[i * PARAMS_N + j];
-                    sum[0] += sp * a_cols_t[(k + 0) * PARAMS_N + j];
-                    sum[1] += sp * a_cols_t[(k + 1) * PARAMS_N + j];
-                    sum[2] += sp * a_cols_t[(k + 2) * PARAMS_N + j];
-                    sum[3] += sp * a_cols_t[(k + 3) * PARAMS_N + j];
+                    sum[0] += (uint16_t)(sp * (uint32_t)a_cols_t[(k + 0) * PARAMS_N + j]);
+                    sum[1] += (uint16_t)(sp * (uint32_t)a_cols_t[(k + 1) * PARAMS_N + j]);
+                    sum[2] += (uint16_t)(sp * (uint32_t)a_cols_t[(k + 2) * PARAMS_N + j]);
+                    sum[3] += (uint16_t)(sp * (uint32_t)a_cols_t[(k + 3) * PARAMS_N + j]);
                 }
                 out[i * PARAMS_N + kk + k + 0] += sum[0];
                 out[i * PARAMS_N + kk + k + 2] += sum[2];
diff --git a/crypto_kem/frodokem976shake/opt/matrix_shake.c b/crypto_kem/frodokem976shake/opt/matrix_shake.c
index 43cf3fd2..80826ca5 100644
--- a/crypto_kem/frodokem976shake/opt/matrix_shake.c
+++ b/crypto_kem/frodokem976shake/opt/matrix_shake.c
@@ -96,7 +96,7 @@ int PQCLEAN_FRODOKEM976SHAKE_OPT_mul_add_sa_plus_e(uint16_t *out, const uint16_t
             for (j = 0; j < 4; j++) {
                 uint16_t sp = s[i * PARAMS_N + kk + j];
                 for (k = 0; k < PARAMS_N; k++) {                // Matrix-vector multiplication
-                    sum[k] += sp * a_cols[(t + j) * PARAMS_N + k];
+                    sum[k] += (uint16_t)(sp * (uint32_t)a_cols[(t + j) * PARAMS_N + k]);
                 }
             }
             for (k = 0; k < PARAMS_N; k++) {