diff --git a/owrx/map.py b/owrx/map.py
index 9dc5c48..081a691 100644
--- a/owrx/map.py
+++ b/owrx/map.py
@@ -25,13 +25,23 @@ class Map(object):
     def __init__(self):
         self.clients = []
         self.positions = {}
+        self.positionsLock = threading.Lock()
 
         def removeLoop():
+            loops = 0
             while True:
                 try:
                     self.removeOldPositions()
                 except Exception:
                     logger.exception("error while removing old map positions")
+                loops += 1
+                # rebuild the positions dictionary every once in a while, it consumes lots of memory otherwise
+                if loops == 60:
+                    try:
+                        self.rebuildPositions()
+                    except Exception:
+                        logger.exception("error while rebuilding positions")
+                    loops = 0
                 time.sleep(60)
 
         threading.Thread(target=removeLoop, daemon=True).start()
@@ -64,7 +74,8 @@ class Map(object):
 
     def updateLocation(self, callsign, loc: Location, mode: str, band: Band = None):
         ts = datetime.now()
-        self.positions[callsign] = {"location": loc, "updated": ts, "mode": mode, "band": band}
+        with self.positionsLock:
+            self.positions[callsign] = {"location": loc, "updated": ts, "mode": mode, "band": band}
         self.broadcast(
             [
                 {
@@ -80,13 +91,15 @@ class Map(object):
     def touchLocation(self, callsign):
         # not implemented on the client side yet, so do not use!
         ts = datetime.now()
-        if callsign in self.positions:
-            self.positions[callsign]["updated"] = ts
+        with self.positionsLock:
+            if callsign in self.positions:
+                self.positions[callsign]["updated"] = ts
         self.broadcast([{"callsign": callsign, "lastseen": ts.timestamp() * 1000}])
 
     def removeLocation(self, callsign):
-        self.positions.pop(callsign, None)
-        # TODO broadcast removal to clients
+        with self.positionsLock:
+            del self.positions[callsign]
+            # TODO broadcast removal to clients
 
     def removeOldPositions(self):
         pm = PropertyManager.getSharedInstance()
@@ -97,6 +110,11 @@ class Map(object):
         for callsign in to_be_removed:
             self.removeLocation(callsign)
 
+    def rebuildPositions(self):
+        with self.positionsLock:
+            p = {key: value for key, value in self.positions.items()}
+            self.positions = p
+
 
 class LatLngLocation(Location):
     def __init__(self, lat: float, lon: float):