diff --git a/source/arch/intel/encoding_avx2.c b/source/arch/intel/encoding_avx2.c
index 439d6ddad..92c4abdfa 100644
--- a/source/arch/intel/encoding_avx2.c
+++ b/source/arch/intel/encoding_avx2.c
@@ -194,13 +194,13 @@ static inline bool decode(const unsigned char *in, unsigned char *out) {
 
 size_t aws_common_private_base64_decode_sse41(const unsigned char *in, unsigned char *out, size_t len) {
     if (len % 4) {
-        return (size_t)-1;
+        return SIZE_MAX;
     }
 
     size_t outlen = 0;
     while (len > 32) {
         if (!decode(in, out)) {
-            return (size_t)-1;
+            return SIZE_MAX;
         }
         len -= 32;
         in += 32;
@@ -230,13 +230,13 @@ size_t aws_common_private_base64_decode_sse41(const unsigned char *in, unsigned
         }
 
         if (!decode(tmp_in, tmp_out)) {
-            return (size_t)-1;
+            return SIZE_MAX;
         }
 
         /* Check that there are no trailing ones bits */
         for (size_t i = final_out; i < sizeof(tmp_out); i++) {
             if (tmp_out[i]) {
-                return (size_t)-1;
+                return SIZE_MAX;
             }
         }
 
diff --git a/source/encoding.c b/source/encoding.c
index bc860aa4b..97b99145d 100644
--- a/source/encoding.c
+++ b/source/encoding.c
@@ -23,7 +23,7 @@ static inline size_t aws_common_private_base64_decode_sse41(const unsigned char
     (void)out;
     (void)len;
     AWS_ASSERT(false);
-    return (size_t)-1; /* unreachable */
+    return SIZE_MAX; /* unreachable */
 }
 static inline void aws_common_private_base64_encode_sse41(const unsigned char *in, unsigned char *out, size_t len) {
     (void)in;
@@ -361,7 +361,7 @@ int aws_base64_decode(const struct aws_byte_cursor *AWS_RESTRICT to_decode, stru
 
     if (aws_common_private_has_avx2()) {
         size_t result = aws_common_private_base64_decode_sse41(to_decode->ptr, output->buffer, to_decode->len);
-        if (result == -1) {
+        if (result == SIZE_MAX) {
             return aws_raise_error(AWS_ERROR_INVALID_BASE64_STR);
         }
 
diff --git a/tests/atomics_test.c b/tests/atomics_test.c
index f1cf15848..16590a794 100644
--- a/tests/atomics_test.c
+++ b/tests/atomics_test.c
@@ -272,7 +272,7 @@ static int run_races(
     int *participant_indexes = alloca(n_participants_local * sizeof(*participant_indexes));
     struct aws_thread *threads = alloca(n_participants_local * sizeof(struct aws_thread));
 
-    *last_race = (size_t)-1;
+    *last_race = SIZE_MAX;
     n_participants = n_participants_local;
     done_racing = false;
     aws_atomic_init_int(&last_race_index, 0);
@@ -293,7 +293,7 @@ static int run_races(
         *last_race = n_races;
     } else {
         *last_race = (size_t)aws_atomic_load_int_explicit(&last_race_index, aws_memory_order_relaxed);
-        if (*last_race == (size_t)-1) {
+        if (*last_race == SIZE_MAX) {
             /* We didn't even see the first race complete */
             *last_race = 0;
         }