diff --git a/plugins/python/regress/iohelpers.c b/plugins/python/regress/iohelpers.c
index 5dee46a79..9303beb9d 100644
--- a/plugins/python/regress/iohelpers.c
+++ b/plugins/python/regress/iohelpers.c
@@ -141,31 +141,23 @@ char *
 str_replaced(const char *source, size_t dest_len, const char *old, const char *new)
 {
     char *result = calloc(1, dest_len);
+    char *dest = result;
     char *pos = NULL;
     size_t old_len = strlen(old);
-    size_t new_len = strlen(new);
-    size_t available_len = dest_len;
 
     while ((pos = strstr(source, old)) != NULL) {
-        size_t skipped_len = (size_t)(pos - source);
-        if (available_len <= skipped_len + 1)
+        size_t len = snprintf(dest, dest_len,
+            "%.*s%s", (int)(pos - source), source, new);
+        if (len >= dest_len)
             goto fail;
 
-        available_len -= skipped_len;
-        strncat(result, source, skipped_len);
-
-        if (available_len <= new_len + 1)
-            goto fail;
-
-        available_len -= new_len;
-        strcat(result, new);
-
+        dest_len -= len;
+        dest += len;
         source = pos + old_len;
     }
 
-    if (available_len <= strlen(source) + 1)
+    if (strlcpy(dest, source, dest_len) >= dest_len)
         goto fail;
-    strcat(result, source);
 
     return result;
 
diff --git a/plugins/python/regress/testhelpers.c b/plugins/python/regress/testhelpers.c
index a750151b8..33d57ad22 100644
--- a/plugins/python/regress/testhelpers.c
+++ b/plugins/python/regress/testhelpers.c
@@ -44,12 +44,11 @@ const char *
 expected_path(const char *format, ...)
 {
     static char expected_output_file[PATH_MAX];
-    int count = snprintf(expected_output_file, PATH_MAX, TESTDATA_DIR);
-    char *filename = expected_output_file + count;
+    size_t dirlen = strlcpy(expected_output_file, TESTDATA_DIR, sizeof(expected_output_file));
 
     va_list args;
     va_start(args, format);
-    vsprintf(filename, format, args);
+    vsnprintf(expected_output_file + dirlen, PATH_MAX - dirlen, format, args);
     va_end(args);
 
     return expected_output_file;
@@ -213,10 +212,9 @@ verify_log_lines(const char *reference_path)
 
         char *line_end = strstr(line_data, " object at "); // this skips checking the pointer hex
         if (line_end)
-            sprintf(line_end, " object>\n");
+            snprintf(line_end, sizeof(line) - (line_end - line), " object>\n");
 
-        VERIFY_TRUE(strlen(stored_str) + strlen(line_data) + 1 < sizeof(stored_str));  // we have enough space in buffer
-        strcat(stored_str, line_data);
+        VERIFY_TRUE(strlcat(stored_str, line_data, sizeof(stored_str)) < sizeof(stored_str));  // we have enough space in buffer
     }
 
     clean_output(stored_str);