diff --git a/dump1090.h b/dump1090.h
index 979570e..5f8ce7f 100644
--- a/dump1090.h
+++ b/dump1090.h
@@ -164,6 +164,7 @@
 #define MODES_ACFLAGS_NSEWSPD_VALID  (1<<14) // Aircraft EW and NS Speed is known
 #define MODES_ACFLAGS_LATLON_REL_OK  (1<<15) // Indicates it's OK to do a relative CPR
 #define MODES_ACFLAGS_REL_CPR_USED   (1<<16) // Lat/lon derived from relative CPR
+#define MODES_ACFLAGS_NON_ICAO       (1<<17) // Address is not ICAO-format
 
 #define MODES_ACFLAGS_LLEITHER_VALID (MODES_ACFLAGS_LLEVEN_VALID | MODES_ACFLAGS_LLODD_VALID)
 #define MODES_ACFLAGS_LLBOTH_VALID   (MODES_ACFLAGS_LLEVEN_VALID | MODES_ACFLAGS_LLODD_VALID)
diff --git a/interactive.c b/interactive.c
index eee61f5..fc44b38 100644
--- a/interactive.c
+++ b/interactive.c
@@ -601,8 +601,9 @@ void interactiveShowData(void) {
                         snprintf(strFl, 6, "%5d", altitude);
                     }
 
-                    printf("%06X  %-4s  %-4s  %-8s %5s  %3s  %3s  %7s %8s %5.1f %5d %2d\n",
-                           a->addr, strMode, strSquawk, a->flight, strFl, strGs, strTt,
+                    printf("%06X%s %-4s  %-4s  %-8s %5s  %3s  %3s  %7s %8s %5.1f %5d %2d\n",
+                           a->addr, (a->bFlags & MODES_ACFLAGS_NON_ICAO) ? "~" : " ",
+                           strMode, strSquawk, a->flight, strFl, strGs, strTt,
                            strLat, strLon, 10 * log10(signalAverage), msgs, (int)(now - a->seen));
                 }
                 count++;
diff --git a/mode_ac.c b/mode_ac.c
index b168e37..04e522d 100644
--- a/mode_ac.c
+++ b/mode_ac.c
@@ -371,6 +371,7 @@ void decodeModeAMessage(struct modesMessage *mm, int ModeA)
   // Set the Identity field to ModeA
   mm->modeA   = ModeA & 0x7777;
   mm->bFlags |= MODES_ACFLAGS_SQUAWK_VALID;
+  mm->bFlags |= MODES_ACFLAGS_NON_ICAO;
 
   // Flag ident in flight status
   mm->fs = ModeA & 0x0080;
diff --git a/mode_s.c b/mode_s.c
index 1271d7d..0df3d4a 100644
--- a/mode_s.c
+++ b/mode_s.c
@@ -543,7 +543,10 @@ int decodeModesMessage(struct modesMessage *mm, unsigned char *msg)
     // AA (Address announced)
     if (mm->msgtype == 11 || mm->msgtype == 17 || mm->msgtype == 18) {
         mm->addr  = (msg[1] << 16) | (msg[2] << 8) | (msg[3]);
-        if (!mm->correctedbits && (mm->msgtype != 11 || mm->iid == 0)) {            
+
+        if (mm->msgtype == 18 && (mm->cf != 0 && mm->cf != 6))
+            mm->bFlags |= MODES_ACFLAGS_NON_ICAO; // DF 18 message not using ICAO addressing
+        else if (!mm->correctedbits && (mm->msgtype != 11 || mm->iid == 0)) {
             // No CRC errors seen, and either it was an DF17/18 extended squitter
             // or a DF11 acquisition squitter with II = 0. We probably have the right address.