diff --git a/rasterio/merge.py b/rasterio/merge.py
index 7b84797e..0f870d46 100644
--- a/rasterio/merge.py
+++ b/rasterio/merge.py
@@ -11,7 +11,7 @@ import numpy as np
 import rasterio
 from rasterio.coords import disjoint_bounds
 from rasterio.enums import Resampling
-from rasterio.errors import RasterioDeprecationWarning
+from rasterio.errors import RasterioDeprecationWarning, RasterioError
 from rasterio import windows
 from rasterio.transform import Affine
 
@@ -219,6 +219,7 @@ def merge(
 
     with dataset_opener(datasets[0]) as first:
         first_profile = first.profile
+        first_crs = first.crs
         first_res = first.res
         nodataval = first.nodatavals[0]
         dt = first.dtypes[0]
@@ -324,10 +325,17 @@ def merge(
             # This approach uses the maximum amount of memory to solve the
             # problem. Making it more efficient is a TODO.
 
+            # 0. Precondition checks
+            #    - Check that source is within destination bounds
+            #    - Check that CRS is same
+
             if disjoint_bounds((dst_w, dst_s, dst_e, dst_n), src.bounds):
                 logger.debug("Skipping source: src=%r, window=%r", src)
                 continue
 
+            if first_crs != src.crs:
+                raise RasterioError(f"CRS mismatch with source: {dataset}")
+
             # 1. Compute spatial intersection of destination and source
             src_w, src_s, src_e, src_n = src.bounds
 
diff --git a/tests/test_merge.py b/tests/test_merge.py
index e8364376..01c0d3f6 100644
--- a/tests/test_merge.py
+++ b/tests/test_merge.py
@@ -9,6 +9,8 @@ import pytest
 import affine
 import rasterio
 from rasterio.merge import merge
+from rasterio.crs import CRS
+from rasterio.errors import RasterioError
 
 # Non-coincident datasets test fixture.
 # Three overlapping GeoTIFFs, two to the NW and one to the SE.
@@ -42,6 +44,19 @@ def test_data_dir_overlapping(tmp_path):
     return tmp_path
 
 
+def test_different_crs(test_data_dir_overlapping):
+    inputs = [x.name for x in test_data_dir_overlapping.iterdir()]
+
+    # Create new raster with different crs
+    with rasterio.open(test_data_dir_overlapping.joinpath(inputs[-1])) as ds_src:
+        kwds = ds_src.profile
+        kwds['crs'] = CRS.from_epsg(3499)
+        with rasterio.open(test_data_dir_overlapping.joinpath("new.tif"), 'w', **kwds) as ds_out:
+            ds_out.write(ds_src.read())
+    with pytest.raises(RasterioError):
+        result = merge(list(test_data_dir_overlapping.iterdir()))
+
+
 @pytest.mark.parametrize(
     "method,value",
     [("first", 1), ("last", 2), ("min", 1), ("max", 3), ("sum", 6), ("count", 3)],