diff --git a/README-json.md b/README-json.md
index 9e6ecff..5ab71a5 100644
--- a/README-json.md
+++ b/README-json.md
@@ -81,6 +81,8 @@ This file contains dump1090's list of recently seen aircraft. The keys are:
    * sil_type: interpretation of SIL: unknown, perhour, persample
    * gva: Geometric Vertical Accuracy  (2.2.3.2.7.2.8)
    * sda: System Design Assurance (2.2.3.2.7.2.4.6)
+   * modea: true if we seem to be also receiving Mode A responses from this aircraft
+   * modec: true if we seem to be also receiving Mode C responses from this aircraft
    * mlat: list of fields derived from MLAT data
    * tisb: list of fields derived from TIS-B data
    * messages: total number of Mode S messages received from this aircraft
diff --git a/net_io.c b/net_io.c
index 1de5851..ffafed1 100644
--- a/net_io.c
+++ b/net_io.c
@@ -1457,6 +1457,10 @@ char *generateAircraftJson(const char *url_path, int *len) {
             p = safe_snprintf(p, end, ",\"gva\":%u", a->gva);
         if (trackDataValid(&a->sda_valid))
             p = safe_snprintf(p, end, ",\"sda\":%u", a->sda);
+        if (a->modeA_hit)
+            p = safe_snprintf(p, end, ",\"modea\":true");
+        if (a->modeC_hit)
+            p = safe_snprintf(p, end, ",\"modec\":true");
 
 
         p = safe_snprintf(p, end, ",\"mlat\":");