diff --git a/test/test_expression.py b/test/test_expression.py
index cbbed2a35..1b973e9a6 100644
--- a/test/test_expression.py
+++ b/test/test_expression.py
@@ -642,6 +642,81 @@ def test_np_bool_handling(ctx_factory):
     assert out.get().item() is True
 
 
+@pytest.mark.parametrize("target", [lp.PyOpenCLTarget, lp.ExecutableCTarget])
+def test_complex_functions_with_real_args(ctx_factory, target):
+    # Reported by David Ham. See <https://github.com/inducer/loopy/issues/851>
+    t_unit = lp.make_kernel(
+            "{[i]: 0<=i<10}",
+            """
+            y1[i] = abs(c64[i])
+            y2[i] = real(c64[i])
+            y3[i] = imag(c64[i])
+            y4[i] = conj(c64[i])
+
+            y5[i] = abs(c128[i])
+            y6[i] = real(c128[i])
+            y7[i] = imag(c128[i])
+            y8[i] = conj(c128[i])
+
+
+            y9[i] = abs(f32[i])
+            y10[i] = real(f32[i])
+            y11[i] = imag(f32[i])
+            y12[i] = conj(f32[i])
+
+            y13[i] = abs(f64[i])
+            y14[i] = real(f64[i])
+            y15[i] = imag(f64[i])
+            y16[i] = conj(f64[i])
+            """,
+            target=target())
+
+    t_unit = lp.add_dtypes(t_unit,
+                           {"y9,y10,y11,y12": np.complex64,
+                            "y13,y14,y15,y16": np.complex128,
+                            "c64": np.complex64,
+                            "c128": np.complex128,
+                            "f64": np.float64,
+                            "f32": np.float32})
+    t_unit = lp.set_options(t_unit, return_dict=True)
+
+    from numpy.random import default_rng
+    rng = default_rng(0)
+    c64 = (rng.random(10, dtype=np.float32)
+           + np.csingle(1j)*rng.random(10, dtype=np.float32))
+    c128 = (rng.random(10, dtype=np.float64)
+            + np.cdouble(1j)*rng.random(10, dtype=np.float64))
+    f32 = rng.random(10, dtype=np.float32)
+    f64 = rng.random(10, dtype=np.float64)
+
+    if target == lp.PyOpenCLTarget:
+        cl_ctx = ctx_factory()
+        with cl.CommandQueue(cl_ctx) as queue:
+            evt, out = t_unit(queue, c64=c64, c128=c128, f32=f32, f64=f64)
+    elif target == lp.ExecutableCTarget:
+        t_unit = lp.set_options(t_unit, build_options=["-Werror"])
+        evt, out = t_unit(c64=c64, c128=c128, f32=f32, f64=f64)
+    else:
+        raise NotImplementedError("unsupported target")
+
+    np.testing.assert_allclose(out["y1"], np.abs(c64), rtol=1e-6)
+    np.testing.assert_allclose(out["y2"], np.real(c64), rtol=1e-6)
+    np.testing.assert_allclose(out["y3"], np.imag(c64), rtol=1e-6)
+    np.testing.assert_allclose(out["y4"], np.conj(c64), rtol=1e-6)
+    np.testing.assert_allclose(out["y5"], np.abs(c128), rtol=1e-6)
+    np.testing.assert_allclose(out["y6"], np.real(c128), rtol=1e-6)
+    np.testing.assert_allclose(out["y7"], np.imag(c128), rtol=1e-6)
+    np.testing.assert_allclose(out["y8"], np.conj(c128), rtol=1e-6)
+    np.testing.assert_allclose(out["y9"], np.abs(f32), rtol=1e-6)
+    np.testing.assert_allclose(out["y10"], np.real(f32), rtol=1e-6)
+    np.testing.assert_allclose(out["y11"], np.imag(f32), rtol=1e-6)
+    np.testing.assert_allclose(out["y12"], np.conj(f32), rtol=1e-6)
+    np.testing.assert_allclose(out["y13"], np.abs(f64), rtol=1e-6)
+    np.testing.assert_allclose(out["y14"], np.real(f64), rtol=1e-6)
+    np.testing.assert_allclose(out["y15"], np.imag(f64), rtol=1e-6)
+    np.testing.assert_allclose(out["y16"], np.conj(f64), rtol=1e-6)
+
+
 if __name__ == "__main__":
     if len(sys.argv) > 1:
         exec(sys.argv[1])