diff --git a/crypto_kem/frodokem640shake/clean/matrix_shake.c b/crypto_kem/frodokem640shake/clean/matrix_shake.c
index e21d2bc8..78c67174 100644
--- a/crypto_kem/frodokem640shake/clean/matrix_shake.c
+++ b/crypto_kem/frodokem640shake/clean/matrix_shake.c
@@ -17,14 +17,14 @@ int PQCLEAN_FRODOKEM640SHAKE_CLEAN_mul_add_as_plus_e(uint16_t *out, const uint16
     // Generate-and-multiply: generate matrix A (N x N) row-wise, multiply by s on the right.
     // Inputs: s, e (N x N_BAR)
     // Output: out = A*s + e (N x N_BAR)
-    uint16_t i, j, k;
+    int i, j, k;
     int16_t A[PARAMS_N * PARAMS_N] = {0};
 
     uint8_t seed_A_separated[2 + BYTES_SEED_A];
     uint16_t *seed_A_origin = (uint16_t *)&seed_A_separated;
     memcpy(&seed_A_separated[2], seed_A, BYTES_SEED_A);
     for (i = 0; i < PARAMS_N; i++) {
-        seed_A_origin[0] = PQCLEAN_FRODOKEM640SHAKE_CLEAN_UINT16_TO_LE(i);
+        seed_A_origin[0] = PQCLEAN_FRODOKEM640SHAKE_CLEAN_UINT16_TO_LE((uint16_t) i);
         shake128((unsigned char *)(A + i * PARAMS_N), (unsigned long long)(2 * PARAMS_N), seed_A_separated, 2 + BYTES_SEED_A);
     }
     for (i = 0; i < PARAMS_N * PARAMS_N; i++) {
@@ -50,14 +50,14 @@ int PQCLEAN_FRODOKEM640SHAKE_CLEAN_mul_add_sa_plus_e(uint16_t *out, const uint16
     // Generate-and-multiply: generate matrix A (N x N) column-wise, multiply by s' on the left.
     // Inputs: s', e' (N_BAR x N)
     // Output: out = s'*A + e' (N_BAR x N)
-    uint16_t i, j, k;
+    int i, j, k;
     int16_t A[PARAMS_N * PARAMS_N] = {0};
 
     uint8_t seed_A_separated[2 + BYTES_SEED_A];
     uint16_t *seed_A_origin = (uint16_t *)&seed_A_separated;
     memcpy(&seed_A_separated[2], seed_A, BYTES_SEED_A);
     for (i = 0; i < PARAMS_N; i++) {
-        seed_A_origin[0] = PQCLEAN_FRODOKEM640SHAKE_CLEAN_UINT16_TO_LE(i);
+        seed_A_origin[0] = PQCLEAN_FRODOKEM640SHAKE_CLEAN_UINT16_TO_LE((uint16_t) i);
         shake128((unsigned char *)(A + i * PARAMS_N), (unsigned long long)(2 * PARAMS_N), seed_A_separated, 2 + BYTES_SEED_A);
     }
     for (i = 0; i < PARAMS_N * PARAMS_N; i++) {