diff --git a/tests/test_cobs_decode_inc.cc b/tests/test_cobs_decode_inc.cc
index d5ca694..d0cc0ca 100644
--- a/tests/test_cobs_decode_inc.cc
+++ b/tests/test_cobs_decode_inc.cc
@@ -24,7 +24,7 @@ TEST_CASE("cobs_decode_inc") {
                                .dst = dec.data(),
                                .src_max = enc.size(),
                                .dst_max = dec.size() };
-  size_t enc_len, dec_len;
+  size_t enc_len{ 0u }, dec_len{ 0u };
   bool done{ false };
 
   SUBCASE("bad args") {
@@ -65,7 +65,7 @@ TEST_CASE("cobs_decode_inc") {
     REQUIRE(enc_len <= COBS_ENCODE_MAX(dec_len));
 
     byte_vec_t oneshot(enc.size());
-    size_t oneshot_len;
+    size_t oneshot_len{ 0u };
     REQUIRE(
         cobs_decode(enc.data(), enc_len, oneshot.data(), oneshot.size(), &oneshot_len) ==
         COBS_RET_SUCCESS);
@@ -78,7 +78,7 @@ TEST_CASE("cobs_decode_inc") {
       args.src_max = 1;
       args.dst_max = 1;
 
-      size_t this_enc_len, this_dec_len;
+      size_t this_enc_len{ 0u }, this_dec_len{ 0u };
       REQUIRE_MESSAGE(cobs_decode_inc(&ctx, &args, &this_enc_len, &this_dec_len, &done) ==
                           COBS_RET_SUCCESS,
                       cur_dec);
diff --git a/tests/test_cobs_decode_inplace.cc b/tests/test_cobs_decode_inplace.cc
index a9819aa..b690dbc 100644
--- a/tests/test_cobs_decode_inplace.cc
+++ b/tests/test_cobs_decode_inplace.cc
@@ -114,7 +114,7 @@ TEST_CASE("Inplace decoding") {
 namespace {
 void verify_decode_inplace(unsigned char *inplace, size_t payload_len) {
   byte_vec_t external(std::max(payload_len, size_t(1)));
-  size_t external_len;
+  size_t external_len{ 0u };
   REQUIRE_MESSAGE(cobs_decode(inplace,
                               payload_len + 2,
                               external.data(),
diff --git a/tests/test_cobs_encode.cc b/tests/test_cobs_encode.cc
index eefa20b..a9e47d2 100644
--- a/tests/test_cobs_encode.cc
+++ b/tests/test_cobs_encode.cc
@@ -26,7 +26,7 @@ TEST_CASE("Encoding validation") {
 
 TEST_CASE("Simple encodings") {
   byte_t dec[16], enc[16];
-  size_t enc_len;
+  size_t enc_len{ 0u };
 
   SUBCASE("Empty") {
     REQUIRE(cobs_encode(&dec, 0, enc, sizeof(enc), &enc_len) == COBS_RET_SUCCESS);
@@ -94,7 +94,7 @@ TEST_CASE("Simple encodings") {
 namespace {
 byte_vec_t encode(byte_vec_t const &decoded) {
   byte_vec_t enc(COBS_ENCODE_MAX(static_cast<unsigned>(decoded.size())));
-  size_t enc_len;
+  size_t enc_len{ 0u };
   REQUIRE(cobs_encode(decoded.data(), decoded.size(), enc.data(), enc.size(), &enc_len) ==
           COBS_RET_SUCCESS);
   return byte_vec_t(enc.data(), enc.data() + enc_len);