diff --git a/xrspatial/proximity.py b/xrspatial/proximity.py
index 76750c52..6f79f039 100644
--- a/xrspatial/proximity.py
+++ b/xrspatial/proximity.py
@@ -1221,9 +1221,24 @@ def _process_numpy(img, x_coords, y_coords):
     def _process_dask(raster, xs, ys):
 
         if max_distance >= max_possible_distance:
-            # consider all targets in the whole raster
-            # the data array is computed at once,
-            # make sure your data fit your memory
+            # The line-sweep needs the full raster in one chunk.
+            # Guard against OOM before rechunking.
+            estimated_bytes = np.prod(raster.shape) * raster.data.dtype.itemsize
+            # ~35 bytes/pixel working memory (distance, output, pan_near,
+            # scan_line, nearest arrays, etc.)
+            estimated_working = estimated_bytes * 35
+            try:
+                from xrspatial.zonal import _available_memory_bytes
+                avail = _available_memory_bytes()
+            except ImportError:
+                avail = 2 * 1024**3
+            if estimated_working > 0.8 * avail:
+                raise ValueError(
+                    f"proximity() with max_distance >= raster diagonal "
+                    f"needs ~{estimated_working / 1e9:.1f} GB but only "
+                    f"~{avail / 1e9:.1f} GB available.  Set a finite "
+                    f"max_distance for out-of-core dask processing."
+                )
             height, width = raster.shape
             raster.data = raster.data.rechunk({0: height, 1: width})
             xs = xs.rechunk({0: height, 1: width})
diff --git a/xrspatial/tests/test_proximity.py b/xrspatial/tests/test_proximity.py
index 41aa69af..5469fd06 100644
--- a/xrspatial/tests/test_proximity.py
+++ b/xrspatial/tests/test_proximity.py
@@ -374,6 +374,30 @@ def _make_kdtree_raster(height=20, width=30, chunks=(10, 15)):
     return raster
 
 
+@pytest.mark.skipif(da is None, reason="dask is not installed")
+def test_proximity_dask_inf_distance_memory_guard():
+    """Line-sweep path with inf max_distance should raise when memory is tight."""
+    from unittest.mock import patch
+    from xrspatial.proximity import _available_memory_bytes
+
+    data = np.zeros((100, 100), dtype=np.float64)
+    data[50, 50] = 1.0
+    raster = xr.DataArray(
+        da.from_array(data, chunks=(50, 50)),
+        dims=['y', 'x'],
+        coords={
+            'x': np.linspace(-10, 10, 100),
+            'y': np.linspace(-5, 5, 100),
+        },
+    )
+
+    # Force the non-KDTree path by using GREAT_CIRCLE metric
+    # (KDTree only supports EUCLIDEAN/MANHATTAN), and mock tight memory.
+    with patch('xrspatial.proximity._available_memory_bytes', return_value=1024):
+        with pytest.raises(MemoryError, match="exceed available memory"):
+            proximity(raster, target_values=[1], distance_metric="GREAT_CIRCLE")
+
+
 @pytest.mark.skipif(da is None, reason="dask is not installed")
 @pytest.mark.parametrize("metric", ["EUCLIDEAN", "MANHATTAN"])
 def test_proximity_dask_kdtree_matches_numpy(metric):