diff --git a/.clang-tidy.yml b/.clang-tidy.yml
index 83052420de..b22fdc6a4f 100644
--- a/.clang-tidy.yml
+++ b/.clang-tidy.yml
@@ -39,6 +39,7 @@ Checks:
   - readability-redundant-function-ptr-dereference
   - readability-redundant-parentheses
   - readability-redundant-preprocessor
+  - readability-suspicious-call-argument
   - readability-uppercase-literal-suffix
 
 CheckOptions:
diff --git a/lib/curlx/strerr.c b/lib/curlx/strerr.c
index e3e838d8c0..91a329e915 100644
--- a/lib/curlx/strerr.c
+++ b/lib/curlx/strerr.c
@@ -44,7 +44,6 @@
 static const char *get_winsock_error(int err, char *buf, size_t len)
 {
   VERBOSE(const char *p);
-  VERBOSE(size_t alen);
 
   if(!len)
     return NULL;
@@ -221,8 +220,7 @@ static const char *get_winsock_error(int err, char *buf, size_t len)
   default:
     return NULL;
   }
-  alen = strlen(p);
-  curlx_strcopy(buf, len, p, alen);
+  curlx_strcopy(buf, len, p, strlen(p));
   return buf;
 #endif
 }
diff --git a/tests/libtest/cli_hx_download.c b/tests/libtest/cli_hx_download.c
index 9c4d99e499..5817e06756 100644
--- a/tests/libtest/cli_hx_download.c
+++ b/tests/libtest/cli_hx_download.c
@@ -85,10 +85,10 @@ static size_t my_write_d_cb(char *buf, size_t nitems, size_t buflen,
                             void *userdata)
 {
   struct transfer_d *t = userdata;
-  size_t blen = (nitems * buflen);
+  curl_off_t blen = nitems * buflen;
   size_t nwritten;
 
-  curl_mfprintf(stderr, "[t-%zu] RECV %zu bytes, "
+  curl_mfprintf(stderr, "[t-%zu] RECV %" CURL_FORMAT_CURL_OFF_T " bytes, "
                 "total=%" CURL_FORMAT_CURL_OFF_T ", "
                 "pause_at=%" CURL_FORMAT_CURL_OFF_T "\n",
                 t->idx, blen, t->recv_size, t->pause_at);
@@ -108,19 +108,19 @@ static size_t my_write_d_cb(char *buf, size_t nitems, size_t buflen,
     return CURL_WRITEFUNC_PAUSE;
   }
 
-  nwritten = fwrite(buf, nitems, buflen, t->out);
-  if(nwritten < blen) {
+  nwritten = fwrite(buf, buflen, nitems, t->out);
+  if(nwritten < nitems) {
     curl_mfprintf(stderr, "[t-%zu] write failure\n", t->idx);
     return 0;
   }
-  t->recv_size += (curl_off_t)nwritten;
+  t->recv_size += blen;
   if(t->fail_at > 0 && t->recv_size >= t->fail_at) {
     curl_mfprintf(stderr, "[t-%zu] FAIL by write callback at "
                   "%" CURL_FORMAT_CURL_OFF_T " bytes\n", t->idx, t->recv_size);
     return CURL_WRITEFUNC_ERROR;
   }
 
-  return nwritten;
+  return (size_t)blen;
 }
 
 static int my_progress_d_cb(void *userdata,
diff --git a/tests/libtest/cli_hx_upload.c b/tests/libtest/cli_hx_upload.c
index b5fd1c642c..a0575c24e4 100644
--- a/tests/libtest/cli_hx_upload.c
+++ b/tests/libtest/cli_hx_upload.c
@@ -64,10 +64,10 @@ static size_t my_write_u_cb(char *buf, size_t nitems, size_t buflen,
                             void *userdata)
 {
   struct transfer_u *t = userdata;
-  size_t blen = (nitems * buflen);
+  curl_off_t blen = nitems * buflen;
   size_t nwritten;
 
-  curl_mfprintf(stderr, "[t-%zu] RECV %zu bytes, "
+  curl_mfprintf(stderr, "[t-%zu] RECV %" CURL_FORMAT_CURL_OFF_T " bytes, "
                 "total=%" CURL_FORMAT_CURL_OFF_T ", "
                 "pause_at=%" CURL_FORMAT_CURL_OFF_T "\n",
                 t->idx, blen, t->recv_size, t->pause_at);
@@ -79,13 +79,13 @@ static size_t my_write_u_cb(char *buf, size_t nitems, size_t buflen,
       return 0;
   }
 
-  nwritten = fwrite(buf, nitems, buflen, t->out);
-  if(nwritten < blen) {
+  nwritten = fwrite(buf, buflen, nitems, t->out);
+  if(nwritten < nitems) {
     curl_mfprintf(stderr, "[t-%zu] write failure\n", t->idx);
     return 0;
   }
-  t->recv_size += (curl_off_t)nwritten;
-  return nwritten;
+  t->recv_size += blen;
+  return (size_t)blen;
 }
 
 static size_t my_read_cb(char *buf, size_t nitems, size_t buflen,