diff --git a/src/simplex.cc b/src/simplex.cc
index fc47b867..9b0b2411 100644
--- a/src/simplex.cc
+++ b/src/simplex.cc
@@ -56,7 +56,8 @@ SimplexDecoder::SimplexDecoder(SimplexConfig _config) : config(_config) {
 
   std::vector<double> detector_t_coords(config.dem.count_detectors(), 0);
   std::vector<std::vector<double>> detector_coords = get_detector_coords(config.dem);
-  for (size_t d = 0; d < detector_coords.size(); ++d) {
+  size_t num_dets = std::min(detector_coords.size(), detector_t_coords.size());
+  for (size_t d = 0; d < num_dets; ++d) {
     if (detector_coords[d].size() > T_COORD) {
       detector_t_coords[d] = detector_coords[d][T_COORD];
     }
diff --git a/src/tesseract.test.cc b/src/tesseract.test.cc
index fd0d471e..a9278aa8 100644
--- a/src/tesseract.test.cc
+++ b/src/tesseract.test.cc
@@ -559,3 +559,19 @@ TEST(tesseract, MoreThan64Observables) {
     ASSERT_EQ(flipped[i], i);
   }
 }
+
+TEST(utils, DuplicateDetectorCoords) {
+  std::string dem_str = "detector(0, 0, 1) D0\ndetector(0, 0, 2) D0\nerror(0.1) D0\n";
+  stim::DetectorErrorModel dem(dem_str.c_str());
+  auto coords = get_detector_coords(dem);
+  ASSERT_EQ(coords.size(), 1);
+  ASSERT_EQ(coords[0].size(), 3);
+  ASSERT_EQ(coords[0][2], 2.0);
+}
+
+TEST(simplex, DuplicateDetectorCoords) {
+  std::string dem_str = "detector(0, 0, 1) D0\ndetector(0, 0, 2) D0\nerror(0.1) D0\n";
+  stim::DetectorErrorModel dem(dem_str.c_str());
+  SimplexConfig config{dem};
+  EXPECT_NO_THROW({ SimplexDecoder decoder(config); });
+}
diff --git a/src/utils.cc b/src/utils.cc
index 56115d4b..32531c0d 100644
--- a/src/utils.cc
+++ b/src/utils.cc
@@ -28,7 +28,9 @@
 #include "stim.h"
 
 std::vector<std::vector<double>> get_detector_coords(const stim::DetectorErrorModel& dem) {
-  std::vector<std::vector<double>> detector_coords;
+  size_t num_detectors = dem.count_detectors();
+  std::vector<std::vector<double>> detector_coords(num_detectors);
+  bool has_any_coords = false;
   for (const stim::DemInstruction& instruction : dem.flattened().instructions) {
     switch (instruction.type) {
       case stim::DemInstructionType::DEM_SHIFT_DETECTORS:
@@ -38,11 +40,16 @@ std::vector<std::vector<double>> get_detector_coords(const stim::DetectorErrorMo
         break;
       }
       case stim::DemInstructionType::DEM_DETECTOR: {
-        std::vector<double> coord;
-        for (const double& t : instruction.arg_data) {
-          coord.push_back(t);
+        has_any_coords = true;
+        std::vector<double> coord(instruction.arg_data.begin(), instruction.arg_data.end());
+        for (const stim::DemTarget& target : instruction.target_data) {
+          if (target.is_relative_detector_id()) {
+            size_t det_id = target.val();
+            if (det_id < num_detectors) {
+              detector_coords[det_id] = coord;
+            }
+          }
         }
-        detector_coords.push_back(coord);
         break;
       }
       case stim::DemInstructionType::DEM_LOGICAL_OBSERVABLE:
@@ -52,6 +59,9 @@ std::vector<std::vector<double>> get_detector_coords(const stim::DetectorErrorMo
             "Unexpected DemInstructionType found in the detector error model.");
     }
   }
+  if (!has_any_coords) {
+    return {};
+  }
   return detector_coords;
 }
 
@@ -148,10 +158,13 @@ static std::vector<std::vector<size_t>> build_det_orders_coordinate(
     for (size_t i = 0; i < detector_coords.at(0).size(); ++i) {
       orientation_vector.push_back(dist(rng));
     }
-    for (size_t i = 0; i < detector_coords.size(); ++i) {
+    size_t num_dets = std::min(detector_coords.size(), inner_products.size());
+    for (size_t i = 0; i < num_dets; ++i) {
       inner_products[i] = 0;
       for (size_t j = 0; j < orientation_vector.size(); ++j) {
-        inner_products[i] += detector_coords[i][j] * orientation_vector[j];
+        if (j < detector_coords[i].size()) {
+          inner_products[i] += detector_coords[i][j] * orientation_vector[j];
+        }
       }
     }
     std::vector<size_t> perm(dem.count_detectors());