diff --git a/frc971/zeroing/zeroing_test.cc b/frc971/zeroing/zeroing_test.cc
index a4ba3d7..819fad0 100644
--- a/frc971/zeroing/zeroing_test.cc
+++ b/frc971/zeroing/zeroing_test.cc
@@ -400,6 +400,7 @@
   constants.index_difference = 10.0;
   constants.measured_index_position = 20.0;
   constants.known_index_pulse = 1;
+  constants.allowable_encoder_error = 0.01;
 
   PositionSensorSimulator sim(constants.index_difference);
 
@@ -447,6 +448,57 @@
                    estimator.GetEstimatorState().position);
 }
 
+// Tests that we can detect when an index pulse occurs where we didn't expect
+// it to for the PulseIndexZeroingEstimator.
+TEST_F(ZeroingTest, TestRelativeEncoderSlipping) {
+  EncoderPlusIndexZeroingConstants constants;
+  constants.index_pulse_count = 3;
+  constants.index_difference = 10.0;
+  constants.measured_index_position = 20.0;
+  constants.known_index_pulse = 1;
+  constants.allowable_encoder_error = 0.05;
+
+  PositionSensorSimulator sim(constants.index_difference);
+
+  const double start_pos =
+      constants.measured_index_position + 0.5 * constants.index_difference;
+
+  for (double direction : {1.0, -1.0}) {
+    sim.Initialize(start_pos, constants.index_difference / 3.0,
+                   constants.measured_index_position);
+
+    PulseIndexZeroingEstimator estimator(constants);
+
+    // Zero the estimator.
+    MoveTo(&sim, &estimator, start_pos - 1 * constants.index_difference);
+    MoveTo(
+        &sim, &estimator,
+        start_pos - constants.index_pulse_count * constants.index_difference);
+    ASSERT_TRUE(estimator.zeroed());
+    ASSERT_FALSE(estimator.error());
+
+    // We have a 5% allowable error so we slip a little bit each time and make
+    // sure that the index pulses are still accepted.
+    for (double error = 0.00;
+         ::std::abs(error) < constants.allowable_encoder_error;
+         error += 0.01 * direction) {
+      sim.Initialize(start_pos, constants.index_difference / 3.0,
+                     constants.measured_index_position +
+                         error * constants.index_difference);
+      MoveTo(&sim, &estimator, start_pos - constants.index_difference);
+      EXPECT_FALSE(estimator.error());
+    }
+
+    // As soon as we hit cross the error margin, we should trigger an error.
+    sim.Initialize(start_pos, constants.index_difference / 3.0,
+                   constants.measured_index_position +
+                       constants.allowable_encoder_error * 1.1 *
+                           constants.index_difference * direction);
+    MoveTo(&sim, &estimator, start_pos - constants.index_difference);
+    ASSERT_TRUE(estimator.error());
+  }
+}
+
 // Tests that an error is detected when the starting position changes too much.
 TEST_F(ZeroingTest, TestHallEffectZeroing) {
   constants::HallEffectZeroingConstants constants;