diff --git a/src/aspire/source/relion.py b/src/aspire/source/relion.py
index 02b8ab9363..99907cbf6a 100644
--- a/src/aspire/source/relion.py
+++ b/src/aspire/source/relion.py
@@ -34,6 +34,7 @@ def __init__(
         max_rows=None,
         symmetry_group=None,
         memory=None,
+        dtype=None,
     ):
         """
         Load STAR file at given filepath
@@ -50,6 +51,9 @@ def __init__(
         :param symmetry_group: A `SymmetryGroup` object or string corresponding to the symmetry of the molecule.
         :param memory: str or None
             The path of the base directory to use as a data store or None. If None is given, no caching is performed.
+        :param dtype: Optional datatype override.
+            Default `None` infers dtype from underlying image (MRC) files.
+            Can be used to upcast STAR files for processing in double precision.
         """
         logger.info(f"Creating ImageSource from STAR file at path {filepath}")
 
@@ -72,12 +76,19 @@ def __init__(
 
         # Get the 'mode' (data type) - TODO: There's probably a more direct way to do this.
         mode = int(mrc.header.mode)
-        dtypes = {0: "int8", 1: "int16", 2: "float32", 6: "uint16"}
+        mrc_dtypes = {0: "int8", 1: "int16", 2: "float32", 6: "uint16"}
         assert (
-            mode in dtypes
-        ), f"Only modes={list(dtypes.keys())} in MRC files are supported for now."
+            mode in mrc_dtypes
+        ), f"Only modes={list(mrc_dtypes.keys())} in MRC files are supported for now."
 
-        dtype = dtypes[mode]
+        mrc_dtype = mrc_dtypes[mode]
+        # Potentially over ride the inferred data type.
+        if dtype is not None and dtype != np.dtype(mrc_dtype):
+            logger.warning(
+                f"Overriding MRC datatype {mrc_dtype} with user supplied {dtype}."
+            )
+        elif dtype is None:
+            dtype = mrc_dtype
 
         shape = mrc.data.shape
         # the code below  accounts for the case where the first MRCS image in the STAR file has one image
diff --git a/tests/test_starfile_stack.py b/tests/test_starfile_stack.py
index 886bceb8f1..c7729fb18f 100644
--- a/tests/test_starfile_stack.py
+++ b/tests/test_starfile_stack.py
@@ -14,10 +14,15 @@
 
 
 class StarFileTestCase(TestCase):
+    # Default dtype (inferred)
+    _dtype = None
+
     def setUpStarFile(self, starfile_name):
         # set up RelionSource object for tests
         with importlib_path(tests.saved_test_data, starfile_name) as starfile:
-            self.src = RelionSource(starfile, data_folder=DATA_DIR, max_rows=12)
+            self.src = RelionSource(
+                starfile, data_folder=DATA_DIR, max_rows=12, dtype=self._dtype
+            )
 
     def setUp(self):
         # this method is used by StarFileMainCase but overridden by StarFileOneImage
@@ -94,3 +99,30 @@ def testMRCSWithOneParticle(self):
         # where there is only one image in the mrcs
         single_image = self.src.images[0].asnumpy()[0]
         self.assertEqual(single_image.shape, (200, 200))
+
+
+class StarFileDtypeOverrideCase64(StarFileMainCase):
+    # Override RelionSource dtype
+    _dtype = np.float64
+
+    def testSourceDtype(self):
+        """Test source identifies as _dtype."""
+        self.assertTrue(self.src.dtype == self._dtype)
+
+    def testImageDtype(self):
+        """Test image returned as _dtype."""
+        self.assertTrue(self.src.images[0].dtype == self._dtype)
+
+    def testRotationsDtype(self):
+        """Test image returned as _dtype."""
+        self.assertTrue(self.src.rotations.dtype == self._dtype)
+
+    def testImageDownsampleDtype(self):
+        """Test downsample pipeline operation returns _dtype."""
+        _src = self.src.downsample(16)
+        self.assertTrue(_src.images[0].dtype == self._dtype)
+
+
+class StarFileDtypeOverrideCase32(StarFileMainCase):
+    # Override RelionSource dtype
+    _dtype = np.float32