diff --git a/test/kepDE.cpp b/test/kepDE.cpp
index c7a72f6d8..fca7bffda 100644
--- a/test/kepDE.cpp
+++ b/test/kepDE.cpp
@@ -76,40 +76,40 @@ TEST_CASE("kepDE def ctor")
     REQUIRE(k.args()[2] == 0_dbl);
 }
 
-#if 0
-
-TEST_CASE("kepF diff")
+TEST_CASE("kepDE diff")
 {
     auto [x, y, z] = make_vars("x", "y", "z");
 
     {
-        REQUIRE(diff(kepF(x, y, z), x)
-                == -cos(kepF(x, y, z)) / (1_dbl - x * sin(kepF(x, y, z)) - y * cos(kepF(x, y, z))));
-        REQUIRE(diff(kepF(x, y, z), y)
-                == sin(kepF(x, y, z)) / (1_dbl - x * sin(kepF(x, y, z)) - y * cos(kepF(x, y, z))));
-        REQUIRE(diff(kepF(x, y, z), z) == 1_dbl / (1_dbl - x * sin(kepF(x, y, z)) - y * cos(kepF(x, y, z))));
-        auto F = kepF(x * x, x * y, x * z);
-        REQUIRE(diff(F, x) == (y * sin(F) - 2_dbl * x * cos(F) + z) / (1_dbl - x * x * sin(F) - x * y * cos(F)));
-        REQUIRE(diff(F, y) == (x * sin(F)) / (1_dbl - x * x * sin(F) - x * y * cos(F)));
+        REQUIRE(diff(kepDE(x, y, z), x)
+                == (cos(kepDE(x, y, z)) - 1_dbl) / (1_dbl + x * sin(kepDE(x, y, z)) - y * cos(kepDE(x, y, z))));
+        REQUIRE(diff(kepDE(x, y, z), y)
+                == -sin(kepDE(x, y, z)) / (1_dbl + x * sin(kepDE(x, y, z)) - y * cos(kepDE(x, y, z))));
+        REQUIRE(diff(kepDE(x, y, z), z) == 1_dbl / (1_dbl + x * sin(kepDE(x, y, z)) - y * cos(kepDE(x, y, z))));
+        auto DE = kepDE(x * x, x * y, x * z);
+        REQUIRE(diff(DE, x)
+                == (2_dbl * x * (cos(DE) - 1_dbl) - y * sin(DE) + z) / (1_dbl + x * x * sin(DE) - x * y * cos(DE)));
+        REQUIRE(diff(DE, y) == (-x * sin(DE)) / (1_dbl + x * x * sin(DE) - x * y * cos(DE)));
     }
 
     {
-        REQUIRE(diff(kepF(par[0], y, z), par[0])
-                == -cos(kepF(par[0], y, z)) / (1_dbl - par[0] * sin(kepF(par[0], y, z)) - y * cos(kepF(par[0], y, z))));
-        REQUIRE(diff(kepF(x, par[1], z), par[1])
-                == sin(kepF(x, par[1], z)) / (1_dbl - x * sin(kepF(x, par[1], z)) - par[1] * cos(kepF(x, par[1], z))));
-        REQUIRE(diff(kepF(x, y, par[2]), par[2])
-                == 1_dbl / (1_dbl - x * sin(kepF(x, y, par[2])) - y * cos(kepF(x, y, par[2]))));
-        auto F = kepF(par[0] * par[0], par[0] * par[1], par[0] * par[2]);
-        REQUIRE(diff(F, par[0])
-                == (par[1] * sin(F) - 2_dbl * par[0] * cos(F) + par[2])
-                       / (1_dbl - par[0] * par[0] * sin(F) - par[0] * par[1] * cos(F)));
-        REQUIRE(diff(F, par[1]) == (par[0] * sin(F)) / (1_dbl - par[0] * par[0] * sin(F) - par[0] * par[1] * cos(F)));
+        REQUIRE(diff(kepDE(par[0], y, z), par[0])
+                == (cos(kepDE(par[0], y, z)) - 1_dbl)
+                       / (1_dbl + par[0] * sin(kepDE(par[0], y, z)) - y * cos(kepDE(par[0], y, z))));
+        REQUIRE(diff(kepDE(x, par[1], z), par[1])
+                == -sin(kepDE(x, par[1], z))
+                       / (1_dbl + x * sin(kepDE(x, par[1], z)) - par[1] * cos(kepDE(x, par[1], z))));
+        REQUIRE(diff(kepDE(x, y, par[2]), par[2])
+                == 1_dbl / (1_dbl + x * sin(kepDE(x, y, par[2])) - y * cos(kepDE(x, y, par[2]))));
+        auto DE = kepDE(par[0] * par[0], par[0] * par[1], par[0] * par[2]);
+        REQUIRE(diff(DE, par[0])
+                == (2_dbl * par[0] * (cos(DE) - 1_dbl) - par[1] * sin(DE) + par[2])
+                       / (1_dbl + par[0] * par[0] * sin(DE) - par[0] * par[1] * cos(DE)));
+        REQUIRE(diff(DE, par[1])
+                == (-par[0] * sin(DE)) / (1_dbl + par[0] * par[0] * sin(DE) - par[0] * par[1] * cos(DE)));
     }
 }
 
-#endif
-
 #define HEYOKA_TEST_KEPDE_OVERLOAD(type)                                                                               \
     {                                                                                                                  \
         auto k = kepDE("x"_var, static_cast<type>(1.1), static_cast<type>(1.3));                                       \