diff --git a/python/lsst/meas/extensions/piff/piffPsfDeterminer.py b/python/lsst/meas/extensions/piff/piffPsfDeterminer.py
index 5560df1..54be841 100644
--- a/python/lsst/meas/extensions/piff/piffPsfDeterminer.py
+++ b/python/lsst/meas/extensions/piff/piffPsfDeterminer.py
@@ -26,6 +26,7 @@
 import galsim
 import re
 import logging
+import yaml
 
 import lsst.utils.logging
 from lsst.afw.cameraGeom import PIXELS, FIELD_ANGLE
@@ -72,24 +73,29 @@ def _validateGalsimInterpolant(name: str) -> bool:
 
 class PiffPsfDeterminerConfig(BasePsfDeterminerTask.ConfigClass):
     spatialOrder = pexConfig.Field[int](
-        doc="specify spatial order for PSF kernel creation",
+        doc="Spatial order for PSF kernel creation. "
+        "Ignored if piffPsfConfigYaml is set.",
         default=2,
     )
     samplingSize = pexConfig.Field[float](
         doc="Resolution of the internal PSF model relative to the pixel size; "
-        "e.g. 0.5 is equal to 2x oversampling",
+        "e.g. 0.5 is equal to 2x oversampling. This affects only the size of "
+        "the PSF model stamp if piffPsfConfigYaml is set.",
         default=1,
     )
     modelSize = pexConfig.Field[int](
-        doc="Internal model size for PIFF (typically odd, but not enforced)",
+        doc="Internal model size for PIFF (typically odd, but not enforced). "
+        "Partially ignored if piffPsfConfigYaml is set.",
         default=25,
     )
     outlierNSigma = pexConfig.Field[float](
-        doc="n sigma for chisq outlier rejection",
+        doc="n sigma for chisq outlier rejection. "
+        "Ignored if piffPsfConfigYaml is set.",
         default=4.0
     )
     outlierMaxRemove = pexConfig.Field[float](
-        doc="Max fraction of stars to remove as outliers each iteration",
+        doc="Max fraction of stars to remove as outliers each iteration. "
+        "Ignored if piffPsfConfigYaml is set.",
         default=0.05
     )
     maxSNR = pexConfig.Field[float](
@@ -109,7 +115,8 @@ class PiffPsfDeterminerConfig(BasePsfDeterminerTask.ConfigClass):
         doc="GalSim interpolant name for Piff to use. "
             "Options include 'Lanczos(N)', where N is an integer, along with "
             "galsim.Cubic, galsim.Delta, galsim.Linear, galsim.Nearest, "
-            "galsim.Quintic, and galsim.SincInterpolant.",
+            "galsim.Quintic, and galsim.SincInterpolant. Ignored if "
+            "piffPsfConfigYaml is set.",
         check=_validateGalsimInterpolant,
         default="Lanczos(11)",
     )
@@ -134,6 +141,12 @@ class PiffPsfDeterminerConfig(BasePsfDeterminerTask.ConfigClass):
         min=0,
         max=3,
     )
+    piffPsfConfigYaml = pexConfig.Field[str](
+        doc="Configuration file for PIFF in YAML format. This overrides many "
+        "other settings in this config and is not validated ahead of runtime.",
+        default=None,
+        optional=True,
+    )
 
     def setDefaults(self):
         super().setDefaults()
@@ -410,24 +423,27 @@ def determinePsf(
             )
             stars.append(piff.Star(data, None))
 
-        piffConfig = {
-            'type': "Simple",
-            'model': {
-                'type': 'PixelGrid',
-                'scale': scale * self.config.samplingSize,
-                'size': self.config.modelSize,
-                'interp': self.config.interpolant
-            },
-            'interp': {
-                'type': 'BasisPolynomial',
-                'order': self.config.spatialOrder
-            },
-            'outliers': {
-                'type': 'Chisq',
-                'nsigma': self.config.outlierNSigma,
-                'max_remove': self.config.outlierMaxRemove
+        if self.config.piffPsfConfigYaml is None:
+            piffConfig = {
+                'type': 'Simple',
+                'model': {
+                    'type': 'PixelGrid',
+                    'scale': scale * self.config.samplingSize,
+                    'size': self.config.modelSize,
+                    'interp': self.config.interpolant,
+                },
+                'interp': {
+                    'type': 'BasisPolynomial',
+                    'order': self.config.spatialOrder,
+                },
+                'outliers': {
+                    'type': 'Chisq',
+                    'nsigma': self.config.outlierNSigma,
+                    'max_remove': self.config.outlierMaxRemove,
+                }
             }
-        }
+        else:
+            piffConfig = yaml.safe_load(self.config.piffPsfConfigYaml)
 
         piffResult = piff.PSF.process(piffConfig)
         wcs = {0: gswcs}
diff --git a/tests/test_psf.py b/tests/test_psf.py
index 291c470..7b2d49d 100644
--- a/tests/test_psf.py
+++ b/tests/test_psf.py
@@ -232,6 +232,7 @@ def setupDeterminer(
         modelSize=25,
         debugStarData=False,
         useCoordinates='pixel',
+        piffPsfConfigYaml=None,
         downsample=False,
         withlog=False,
     ):
@@ -284,6 +285,7 @@ def setupDeterminer(
 
         psfDeterminerConfig.debugStarData = debugStarData
         psfDeterminerConfig.useCoordinates = useCoordinates
+        psfDeterminerConfig.piffPsfConfigYaml = piffPsfConfigYaml
         if downsample:
             psfDeterminerConfig.maxCandidates = 10
         if withlog:
@@ -474,6 +476,10 @@ def testPiffDeterminer_default(self):
     def testPiffDeterminer_stampSize27(self):
         """Test Piff with a psf stampSize of 27."""
         self.checkPiffDeterminer(stampSize=27)
+        self.assertEqual(
+            self.exposure.psf.computeKernelImage(self.exposure.getBBox().getCenter()).getDimensions(),
+            geom.Extent2I(27, 27),
+        )
 
     def testPiffDeterminer_debugStarData(self):
         """Test Piff with debugStarData=True."""
@@ -518,6 +524,32 @@ def testPiffDeterminer_skyCoords_failure(self, angle_degrees=135):
             self.checkPiffDeterminer(useCoordinates='sky', stampSize=15)
 
 
+class piffPsfConfigYamlTestCase(SpatialModelPsfTestCase):
+    """A test case to trigger the codepath that uses piffPsfConfigYaml."""
+
+    def checkPiffDeterminer(self, **kwargs):
+        # Docstring inherited.
+        if "piffPsfConfigYaml" not in kwargs:
+            piffPsfConfigYaml = """
+                # A minimal Piff config corresponding to the defaults.
+                type: Simple
+                model:
+                  type: PixelGrid
+                  scale: 0.2
+                  size: 25
+                  interp: Lanczos(11)
+                interp:
+                  type: BasisPolynomial
+                  order: 1
+                outliers:
+                  type: Chisq
+                  nsigma: 4.0
+                  max_remove: 0.05
+                """
+            kwargs["piffPsfConfigYaml"] = piffPsfConfigYaml
+        return super().checkPiffDeterminer(**kwargs)
+
+
 class PiffConfigTestCase(lsst.utils.tests.TestCase):
     """A test case to check for valid Piff config"""
     def testValidateGalsimInterpolant(self):