diff --git a/src/modules/bppp/tests_impl.h b/src/modules/bppp/tests_impl.h
index 2ee2ac98..a2e29b84 100644
--- a/src/modules/bppp/tests_impl.h
+++ b/src/modules/bppp/tests_impl.h
@@ -103,7 +103,7 @@ static void test_bppp_generators_fixed(void) {
 }
 
 static void test_bppp_tagged_hash(void) {
-    unsigned char tag_data[29] = "Bulletproofs_pp/v0/commitment";
+    unsigned char tag_data[] = {'B', 'u', 'l', 'l', 'e', 't', 'p', 'r', 'o', 'o', 'f', 's', '_', 'p', 'p', '/', 'v', '0', '/', 'c', 'o', 'm', 'm', 'i', 't', 'm', 'e', 'n', 't'};
     secp256k1_sha256 sha;
     secp256k1_sha256 sha_cached;
     unsigned char output[32];
diff --git a/src/modules/ecdsa_adaptor/dleq_impl.h b/src/modules/ecdsa_adaptor/dleq_impl.h
index 2660328c..ff946c2c 100644
--- a/src/modules/ecdsa_adaptor/dleq_impl.h
+++ b/src/modules/ecdsa_adaptor/dleq_impl.h
@@ -18,7 +18,7 @@ static void secp256k1_nonce_function_dleq_sha256_tagged(secp256k1_sha256 *sha) {
 }
 
 /* algo argument for nonce_function_ecdsa_adaptor to derive the nonce using a tagged hash function. */
-static const unsigned char dleq_algo[4] = "DLEQ";
+static const unsigned char dleq_algo[] = {'D','L','E','Q'};
 
 static int secp256k1_dleq_hash_point(secp256k1_sha256 *sha, secp256k1_ge *p) {
     unsigned char buf[33];
diff --git a/src/modules/ecdsa_adaptor/main_impl.h b/src/modules/ecdsa_adaptor/main_impl.h
index 77f1627b..d75764f4 100644
--- a/src/modules/ecdsa_adaptor/main_impl.h
+++ b/src/modules/ecdsa_adaptor/main_impl.h
@@ -98,7 +98,7 @@ static void secp256k1_nonce_function_ecdsa_adaptor_sha256_tagged_aux(secp256k1_s
 }
 
 /* algo argument for nonce_function_ecdsa_adaptor to derive the nonce using a tagged hash function. */
-static const unsigned char ecdsa_adaptor_algo[16] = "ECDSAadaptor/non";
+static const unsigned char ecdsa_adaptor_algo[] = {'E', 'C', 'D', 'S', 'A', 'a', 'd', 'a', 'p', 't', 'o', 'r', '/', 'n', 'o', 'n'};
 
 /* Modified BIP-340 nonce function */
 static int nonce_function_ecdsa_adaptor(unsigned char *nonce32, const unsigned char *msg32, const unsigned char *key32, const unsigned char *pk33, const unsigned char *algo, size_t algolen, void *data) {
diff --git a/src/modules/ecdsa_adaptor/tests_impl.h b/src/modules/ecdsa_adaptor/tests_impl.h
index c3b3d43d..46aec3d7 100644
--- a/src/modules/ecdsa_adaptor/tests_impl.h
+++ b/src/modules/ecdsa_adaptor/tests_impl.h
@@ -730,11 +730,11 @@ static void ecdsa_adaptor_test_sha256_eq(const secp256k1_sha256 *sha1, const sec
 }
 
 static void run_nonce_function_ecdsa_adaptor_tests(void) {
-    unsigned char tag[16] = "ECDSAadaptor/non";
-    unsigned char aux_tag[16] = "ECDSAadaptor/aux";
-    unsigned char algo[16] = "ECDSAadaptor/non";
+    unsigned char tag[] = {'E', 'C', 'D', 'S', 'A', 'a', 'd', 'a', 'p', 't', 'o', 'r', '/', 'n', 'o', 'n'};
+    unsigned char aux_tag[] = {'E', 'C', 'D', 'S', 'A', 'a', 'd', 'a', 'p', 't', 'o', 'r', '/', 'a', 'u', 'x'};
+    unsigned char algo[] = {'E', 'C', 'D', 'S', 'A', 'a', 'd', 'a', 'p', 't', 'o', 'r', '/', 'n', 'o', 'n'};
     size_t algolen = sizeof(algo);
-    unsigned char dleq_tag[4] = "DLEQ";
+    unsigned char dleq_tag[] = {'D', 'L', 'E', 'Q'};
     secp256k1_sha256 sha;
     secp256k1_sha256 sha_optimized;
     unsigned char nonce[32];
diff --git a/src/modules/ecdsa_s2c/tests_impl.h b/src/modules/ecdsa_s2c/tests_impl.h
index 7bbd8770..48f3a3a2 100644
--- a/src/modules/ecdsa_s2c/tests_impl.h
+++ b/src/modules/ecdsa_s2c/tests_impl.h
@@ -10,8 +10,8 @@
 #include "../../../include/secp256k1_ecdsa_s2c.h"
 
 static void test_ecdsa_s2c_tagged_hash(void) {
-    unsigned char tag_data[14] = "s2c/ecdsa/data";
-    unsigned char tag_point[15] = "s2c/ecdsa/point";
+    unsigned char tag_data[] = {'s', '2', 'c', '/', 'e', 'c', 'd', 's', 'a', '/', 'd', 'a', 't', 'a'};
+    unsigned char tag_point[] = {'s', '2', 'c', '/', 'e', 'c', 'd', 's', 'a', '/', 'p', 'o', 'i', 'n', 't'};
     secp256k1_sha256 sha;
     secp256k1_sha256 sha_optimized;
     unsigned char output[32];
@@ -78,10 +78,10 @@ static void run_s2c_opening_test(void) {
 static void test_ecdsa_s2c_api(void) {
     secp256k1_ecdsa_s2c_opening s2c_opening;
     secp256k1_ecdsa_signature sig;
-    const unsigned char msg[32] = "mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm";
-    const unsigned char sec[32] = "ssssssssssssssssssssssssssssssss";
-    const unsigned char s2c_data[32] = "dddddddddddddddddddddddddddddddd";
-    const unsigned char hostrand[32] = "hrhrhrhrhrhrhrhrhrhrhrhrhrhrhrhr";
+    const unsigned char msg[] = {'m', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm', 'm'};
+    const unsigned char sec[] = {'s', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's', 's'};
+    const unsigned char s2c_data[] = {'d', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd', 'd'};
+    const unsigned char hostrand[] = {'h', 'r', 'h', 'r', 'h', 'r', 'h', 'r', 'h', 'r', 'h', 'r', 'h', 'r', 'h', 'r', 'h', 'r', 'h', 'r', 'h', 'r', 'h', 'r', 'h', 'r', 'h', 'r', 'h', 'r', 'h', 'r'};
     unsigned char hostrand_commitment[32];
     secp256k1_pubkey pk;
 
@@ -148,14 +148,14 @@ typedef struct {
 
 static ecdsa_s2c_test ecdsa_s2c_tests[] = {
     {
-        "\x1b\xf6\xfb\x42\xf4\x1e\xb8\x76\xc4\xd7\xaa\x0d\x67\x24\x2b\x00\xba\xab\x99\xdc\x20\x84\x49\x3e\x4e\x63\x27\x7f\xa1\xf7\x7f\x22",
-        "\x03\xf0\x30\xde\xf3\x18\x8c\x0f\x56\xfc\xea\x87\x43\x5b\x30\x76\x43\xf4\x5d\xaf\xe2\x2c\xbc\x82\xfd\x56\x03\x4f\xae\x97\x41\x7d\x3a",
-        "\x02\xdf\x63\x75\x5d\x1f\x32\x92\xbf\xfe\xd8\x29\x86\xb1\x06\x49\x7c\x93\xb1\xf8\xbd\xc0\x45\x4b\x6b\x0b\x0a\x47\x79\xc0\xef\x71\x88",
+        {0x1b, 0xf6, 0xfb, 0x42, 0xf4, 0x1e, 0xb8, 0x76, 0xc4, 0xd7, 0xaa, 0x0d, 0x67, 0x24, 0x2b, 0x00, 0xba, 0xab, 0x99, 0xdc, 0x20, 0x84, 0x49, 0x3e, 0x4e, 0x63, 0x27, 0x7f, 0xa1, 0xf7, 0x7f, 0x22},
+        {0x03, 0xf0, 0x30, 0xde, 0xf3, 0x18, 0x8c, 0x0f, 0x56, 0xfc, 0xea, 0x87, 0x43, 0x5b, 0x30, 0x76, 0x43, 0xf4, 0x5d, 0xaf, 0xe2, 0x2c, 0xbc, 0x82, 0xfd, 0x56, 0x03, 0x4f, 0xae, 0x97, 0x41, 0x7d, 0x3a},
+        {0x02, 0xdf, 0x63, 0x75, 0x5d, 0x1f, 0x32, 0x92, 0xbf, 0xfe, 0xd8, 0x29, 0x86, 0xb1, 0x06, 0x49, 0x7c, 0x93, 0xb1, 0xf8, 0xbd, 0xc0, 0x45, 0x4b, 0x6b, 0x0b, 0x0a, 0x47, 0x79, 0xc0, 0xef, 0x71, 0x88},
     },
     {
-        "\x35\x19\x9a\x8f\xbf\x84\xad\x6e\xf6\x9a\x18\x4c\x1b\x19\x28\x5b\xef\xbe\x06\xe6\x0b\x62\x64\xe6\xd3\x73\x89\x3f\x68\x55\xe2\x4a",
-        "\x03\x90\x17\x17\xce\x7c\x74\x84\xa2\xce\x1b\x7d\xc7\x40\x3b\x14\xe0\x35\x49\x71\x39\x3e\xc0\x92\xa7\xf3\xe0\xc8\xe4\xe2\xd2\x63\x9d",
-        "\x02\xc0\x4a\xc7\xf7\x71\xe8\xeb\xdb\xf3\x15\xff\x5e\x58\xb7\xfe\x95\x16\x10\x21\x03\x50\x00\x66\x17\x2c\x4f\xac\x5b\x20\xf9\xe0\xea",
+        {0x35, 0x19, 0x9a, 0x8f, 0xbf, 0x84, 0xad, 0x6e, 0xf6, 0x9a, 0x18, 0x4c, 0x1b, 0x19, 0x28, 0x5b, 0xef, 0xbe, 0x06, 0xe6, 0x0b, 0x62, 0x64, 0xe6, 0xd3, 0x73, 0x89, 0x3f, 0x68, 0x55, 0xe2, 0x4a},
+        {0x03, 0x90, 0x17, 0x17, 0xce, 0x7c, 0x74, 0x84, 0xa2, 0xce, 0x1b, 0x7d, 0xc7, 0x40, 0x3b, 0x14, 0xe0, 0x35, 0x49, 0x71, 0x39, 0x3e, 0xc0, 0x92, 0xa7, 0xf3, 0xe0, 0xc8, 0xe4, 0xe2, 0xd2, 0x63, 0x9d},
+        {0x02, 0xc0, 0x4a, 0xc7, 0xf7, 0x71, 0xe8, 0xeb, 0xdb, 0xf3, 0x15, 0xff, 0x5e, 0x58, 0xb7, 0xfe, 0x95, 0x16, 0x10, 0x21, 0x03, 0x50, 0x00, 0x66, 0x17, 0x2c, 0x4f, 0xac, 0x5b, 0x20, 0xf9, 0xe0, 0xea},
     },
 };
 
@@ -207,7 +207,7 @@ static void test_ecdsa_s2c_sign_verify(void) {
 
     { /* invalid privkeys */
         unsigned char zero_privkey[32] = {0};
-        unsigned char overflow_privkey[32] = "\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff";
+        unsigned char overflow_privkey[32] = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff};
         CHECK(secp256k1_ecdsa_s2c_sign(CTX, &signature, NULL, message, zero_privkey, s2c_data) == 0);
         CHECK(secp256k1_ecdsa_s2c_sign(CTX, &signature, NULL, message, overflow_privkey, s2c_data) == 0);
     }
diff --git a/src/modules/musig/tests_impl.h b/src/modules/musig/tests_impl.h
index 753b8ac5..d77aed66 100644
--- a/src/modules/musig/tests_impl.h
+++ b/src/modules/musig/tests_impl.h
@@ -579,8 +579,8 @@ static void scriptless_atomic_swap(secp256k1_scratch_space *scratch) {
     int nonce_parity_b;
     unsigned char seed_a[2][32] = { "a0", "a1" };
     unsigned char seed_b[2][32] = { "b0", "b1" };
-    const unsigned char msg32_a[32] = "this is the message blockchain a";
-    const unsigned char msg32_b[32] = "this is the message blockchain b";
+    const unsigned char msg32_a[32] = {'t', 'h', 'i', 's', ' ', 'i', 's', ' ', 't', 'h', 'e', ' ', 'm', 'e', 's', 's', 'a', 'g', 'e', ' ', 'b', 'l', 'o', 'c', 'k', 'c', 'h', 'a', 'i', 'n', ' ', 'a'};
+    const unsigned char msg32_b[32] = {'t', 'h', 'i', 's', ' ', 'i', 's', ' ', 't', 'h', 'e', ' ', 'm', 'e', 's', 's', 'a', 'g', 'e', ' ', 'b', 'l', 'o', 'c', 'k', 'c', 'h', 'a', 'i', 'n', ' ', 'b'};
     int i;
 
     /* Step 1: key setup */
@@ -676,12 +676,12 @@ static void sha256_tag_test_internal(secp256k1_sha256 *sha_tagged, unsigned char
 static void sha256_tag_test(void) {
     secp256k1_sha256 sha_tagged;
     {
-        char tag[11] = "KeyAgg list";
+        char tag[] = {'K', 'e', 'y', 'A', 'g', 'g', ' ', 'l', 'i', 's', 't'};
         secp256k1_musig_keyagglist_sha256(&sha_tagged);
         sha256_tag_test_internal(&sha_tagged, (unsigned char*)tag, sizeof(tag));
     }
     {
-        char tag[18] = "KeyAgg coefficient";
+        char tag[] = {'K', 'e', 'y', 'A', 'g', 'g', ' ', 'c', 'o', 'e', 'f', 'f', 'i', 'c', 'i', 'e', 'n', 't'};
         secp256k1_musig_keyaggcoef_sha256(&sha_tagged);
         sha256_tag_test_internal(&sha_tagged, (unsigned char*)tag, sizeof(tag));
     }
diff --git a/src/modules/rangeproof/tests_impl.h b/src/modules/rangeproof/tests_impl.h
index 49cc16cf..f2ca3214 100644
--- a/src/modules/rangeproof/tests_impl.h
+++ b/src/modules/rangeproof/tests_impl.h
@@ -414,7 +414,7 @@ static void test_single_value_proof(uint64_t val) {
     unsigned char blind[32];
     unsigned char blind_out[32];
     unsigned char nonce[32];
-    const unsigned char message[1] = " "; /* no message will fit into a single-value proof */
+    const unsigned char message[] = { ' ' }; /* no message will fit into a single-value proof */
     unsigned char message_out[sizeof(proof)] = { 0 };
     size_t plen = sizeof(proof);
     uint64_t min_val_out = 0;
diff --git a/src/modules/schnorrsig_halfagg/tests_impl.h b/src/modules/schnorrsig_halfagg/tests_impl.h
index 16ac3ab3..37099849 100644
--- a/src/modules/schnorrsig_halfagg/tests_impl.h
+++ b/src/modules/schnorrsig_halfagg/tests_impl.h
@@ -8,7 +8,7 @@
 /* We test that the hash initialized by secp256k1_schnorrsig_sha256_tagged_aggregate
  * has the expected state. */
 void test_schnorrsig_sha256_tagged_aggregate(void) {
-    unsigned char tag[18] = "HalfAgg/randomizer";
+    unsigned char tag[] = {'H', 'a', 'l', 'f', 'A', 'g', 'g', '/', 'r', 'a', 'n', 'd', 'o', 'm', 'i', 'z', 'e', 'r'};
     secp256k1_sha256 sha;
     secp256k1_sha256 sha_optimized;