diff --git a/tests/jax/test_benchmarks.py b/tests/jax/test_benchmarks.py
index 53e75091..3c773dc6 100644
--- a/tests/jax/test_benchmarks.py
+++ b/tests/jax/test_benchmarks.py
@@ -240,6 +240,25 @@ def test_benchmark_gaussian_init(benchmark, kind):
     print(f"time: {dt:0.4g} ms", end=" ")
 
 
+def _run_benchmark_interpimage_flux_frac(img):
+    x, y = img.get_pixel_centers()
+    cenx = img.center.x
+    ceny = img.center.y
+    return jgs.interpolatedimage._flux_frac(img.array, x, y, cenx, ceny)
+
+
+@pytest.mark.parametrize("kind", ["compile", "run"])
+def test_benchmark_interpimage_flux_frac(benchmark, kind):
+    obj = jgs.Gaussian(half_light_radius=0.9).shear(g1=0.1, g2=0.2)
+    img = obj.drawImage(nx=55, ny=55, scale=0.2, method="no_pixel")
+    dt = _run_benchmarks(
+        benchmark,
+        kind,
+        lambda: _run_benchmark_interpimage_flux_frac(img).block_until_ready(),
+    )
+    print(f"time: {dt:0.4g} ms", end=" ")
+
+
 @jax.jit
 def _run_benchmark_rng_discard(rng):
     rng.discard(1000)
diff --git a/tests/jax/test_interpolatedimage_utils.py b/tests/jax/test_interpolatedimage_utils.py
index 7043615f..56f3ced5 100644
--- a/tests/jax/test_interpolatedimage_utils.py
+++ b/tests/jax/test_interpolatedimage_utils.py
@@ -16,6 +16,7 @@
 from jax_galsim.interpolatedimage import (
     _draw_with_interpolant_kval,
     _draw_with_interpolant_xval,
+    _flux_frac,
 )
 
 
@@ -354,3 +355,76 @@ def test_interpolatedimage_interpolant_sample(interp):
     fdev = np.abs(h - yv) / np.abs(np.sqrt(yv))
     np.testing.assert_allclose(fdev[msk], 0, rtol=0, atol=5.0, err_msg=f"{interp}")
     np.testing.assert_allclose(fdev[~msk], 0, rtol=0, atol=15.0, err_msg=f"{interp}")
+
+
+def test_interpolatedimage_flux_frac():
+    obj = jax_galsim.Gaussian(half_light_radius=0.9).shear(g1=0.1, g2=0.2)
+    img = obj.drawImage(nx=55, ny=55, scale=0.05, method="no_pixel")
+    true_val = [
+        0.02186161,
+        0.06551123,
+        0.10894079,
+        0.15200604,
+        0.19456641,
+        0.23648629,
+        0.27763629,
+        0.31789470,
+        0.35714823,
+        0.39529300,
+        0.43223542,
+        0.46789303,
+        0.50219434,
+        0.53507960,
+        0.56650090,
+        0.59642231,
+        0.62481892,
+        0.65167749,
+        0.67699528,
+        0.70077991,
+        0.72304893,
+        0.74382806,
+        0.76315117,
+        0.78105938,
+        0.79759991,
+        0.81282544,
+        0.82679272,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+        0.83956224,
+    ]
+
+    x, y = img.get_pixel_centers()
+    cenx = img.center.x
+    ceny = img.center.y
+    val = _flux_frac(img.array, x, y, cenx, ceny)
+    np.testing.assert_allclose(
+        val,
+        true_val,
+        rtol=0,
+        atol=1e-6,
+    )