diff --git a/src/rtl_433/r_api.c b/src/rtl_433/r_api.c
index ba3a2d85..ec8c255d 100644
--- a/src/rtl_433/r_api.c
+++ b/src/rtl_433/r_api.c
@@ -798,10 +798,12 @@ void data_acquired_handler(r_device* r_dev, data_t* data) {
       else if ((d->type == DATA_DOUBLE) &&
                (str_endswith(d->key, "_in") || str_endswith(d->key, "_inch"))) {
         d->value.v_dbl = inch2mm(d->value.v_dbl);
-        char* new_label =
-            str_replace(str_replace(d->key, "_inch", "_in"), "_in", "_mm");
+        // need to free ptr returned from str_replace
+        char* new_label1 = str_replace(d->key, "_inch", "_in");
+        char* new_label2 = str_replace(new_label1, "_in", "_mm");
+        free(new_label1);
         free(d->key);
-        d->key = new_label;
+        d->key = new_label2;
         char* new_format_label = str_replace(d->format, "in", "mm");
         free(d->format);
         d->format = new_format_label;