diff --git a/modules/services/osm.js b/modules/services/osm.js
index 00d38e297b9..78fb9054c54 100644
--- a/modules/services/osm.js
+++ b/modules/services/osm.js
@@ -47,6 +47,8 @@ var _rateLimitError;
 var _userChangesets;
 var _userDetails;
 var _off;
+var _isLoading = false;
+var _maxSubdivisionDepth = 3;
 
 // set a default but also load this from the API status
 var _maxWayNodes = 2000;
@@ -553,6 +555,7 @@ export default {
         _userChangesets = undefined;
         _userDetails = undefined;
         _rateLimitError = undefined;
+        _isLoading = false;
 
         Object.values(_tileCache.inflight).forEach(abortRequest);
         Object.values(_noteCache.inflight).forEach(abortRequest);
@@ -1102,11 +1105,13 @@ export default {
 
     // Load a single data tile
     // GET /api/0.6/map?bbox=
-    loadTile: function(tile, callback) {
+    loadTile: function(tile, callback, depth) {
+        depth = depth || 0;
         if (_off) return;
         if (_tileCache.loaded[tile.id] || _tileCache.inflight[tile.id]) return;
 
-        if (!hasInflightRequests(_tileCache)) {
+        if (!hasInflightRequests(_tileCache) && !_isLoading) {
+            _isLoading = true;
             dispatch.call('loading');   // start the spinner
         }
 
@@ -1128,19 +1133,37 @@ export default {
                 bbox.id = tile.id;
                 _tileCache.rtree.insert(bbox);
             } else {
-                // map tile loading error: e.g. network connection error,
-                // 509 Bandwidth Limit Exceeded, 429 Too Many Requests
-                if (!_rateLimitError && err.status === 509 || err.status === 429) {
-                    // show "API rate limiting" warning
+
+                // 400 → subdivision (50k node limit)
+                if (err && err.status === 400) {
+
+                    delete _tileCache.inflight[tile.id];
+                    delete _tileCache.toLoad[tile.id];
+
+                    if (depth < _maxSubdivisionDepth) {
+                        var quadrants = tile.extent.split();
+                        quadrants.forEach(function(extent, i) {
+                            var childTile = {
+                                id: tile.id + '-' + depth + '-' + i,
+                                extent: extent
+                            };
+                            this.loadTile(childTile, callback, depth + 1);
+                        }.bind(this));
+                        return;
+                    }
+
+                } else if (!_rateLimitError && (err.status === 509 || err.status === 429)) {
+
                     _rateLimitError = err;
                     dispatch.call('change');
                     this.reloadApiStatus();
+
                 }
-                setTimeout(() => {
-                    // retry loading the tiles
+
+                setTimeout(function() {
                     delete _tileCache.inflight[tile.id];
-                    this.loadTile(tile, callback);
-                }, 8000);
+                    this.loadTile(tile, callback, depth);
+                }.bind(this), 8000);
             }
             if (callback) {
                 callback(err, Object.assign({ data: parsed }, tile));
@@ -1152,6 +1175,7 @@ export default {
                     dispatch.call('change');
                     this.reloadApiStatus();
                 }
+                _isLoading = false;
                 dispatch.call('loaded');     // stop the spinner
             }
         }
diff --git a/test/spec/services/osm_subdivision.js b/test/spec/services/osm_subdivision.js
new file mode 100644
index 00000000000..57f7aa8be1b
--- /dev/null
+++ b/test/spec/services/osm_subdivision.js
@@ -0,0 +1,97 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import osmService from '../../../modules/services/osm.js';
+import { geoExtent } from '../../../modules/geo/index.js';
+
+describe('OSM 400 tile subdivision', () => {
+
+  let service;
+  let fakeTile;
+
+  beforeEach(() => {
+    service = osmService;
+    service.reset();
+
+    fakeTile = {
+      id: '0,0,16',
+      extent: geoExtent([[0, 0], [1, 1]])
+    };
+  });
+
+
+  it('subdivides only once on initial 400', () => {
+
+    let callCount = 0;
+
+    vi.spyOn(service, 'loadFromAPI').mockImplementation((path, cb) => {
+
+      callCount++;
+
+      // Only first call returns 400
+      if (callCount === 1) {
+        cb({
+          status: 400,
+          statusText: 'You requested too many nodes (limit is 50000)'
+        });
+      } else {
+        cb(null, []); // children succeed
+      }
+
+      return { abort: () => {} }; // important
+    });
+
+    const spy = vi.spyOn(service, 'loadTile');
+
+    service.loadTile(fakeTile, () => {});
+
+    // 1 original + 4 children
+    expect(spy).toHaveBeenCalledTimes(5);
+
+    spy.mockRestore();
+  });
+
+
+  it('does not subdivide beyond max depth', () => {
+
+    vi.spyOn(service, 'loadFromAPI').mockImplementation((path, cb) => {
+      cb({
+        status: 400,
+        statusText: 'You requested too many nodes (limit is 50000)'
+      });
+      return { abort: () => {} };
+    });
+
+    const spy = vi.spyOn(service, 'loadTile');
+
+    service.loadTile(fakeTile, () => {}, 3);
+
+    // should not create children
+    expect(spy).toHaveBeenCalledTimes(1);
+
+    spy.mockRestore();
+  });
+
+
+  it('retries for non-400 errors', () => {
+
+    vi.useFakeTimers();
+
+    let retryTriggered = false;
+
+    vi.spyOn(service, 'loadFromAPI').mockImplementation((path, cb) => {
+      cb({ status: 429 });
+      return { abort: () => {} };
+    });
+
+    const spy = vi.spyOn(service, 'loadTile');
+
+    service.loadTile(fakeTile, () => {});
+
+    vi.runAllTimers();
+
+    expect(spy).toHaveBeenCalled();
+
+    spy.mockRestore();
+    vi.useRealTimers();
+  });
+
+});
\ No newline at end of file