diff --git a/common/DiffractionExperiment.cpp b/common/DiffractionExperiment.cpp
index 76395722..79d3f29e 100644
--- a/common/DiffractionExperiment.cpp
+++ b/common/DiffractionExperiment.cpp
@@ -1487,7 +1487,7 @@ std::vector<DetectorTransformation> DiffractionExperiment::BuildTransformationCh
     if (const auto goniometer = GetGoniometer()) {
         DetectorTransformation axis(goniometer->GetName(), TransformationType::Rotation,
                                     goniometer->GetAxis());
-        if (goniometer->IsScanning() && (image_num > 0))
+        if (image_num > 0)
             axis.Values(to_float(goniometer->GetAngleContainer(image_num)));
         else
             axis.Value(goniometer->GetStart_deg());
@@ -1498,12 +1498,15 @@ std::vector<DetectorTransformation> DiffractionExperiment::BuildTransformationCh
         add(DetectorTransformation("omega", TransformationType::Rotation, {-1, 0, 0}).Value(0.0f));
     }
 
-    // Smargon chi and phi are ordinary axes that happen not to move.
+    // Smargon chi and phi are ordinary axes that happen not to move. They still carry one entry per
+    // image: a reader takes the number of images from the innermost axis of the sample chain when no
+    // axis varies, and chi/phi are innermost whenever they are present.
     if (const auto smargon = dataset.GetSmargonPosition()) {
+        const auto n = static_cast<size_t>(std::max<int64_t>(image_num, 1));
         add(DetectorTransformation("chi", TransformationType::Rotation, smargon->chi_axis)
-                    .Value(smargon->chi_deg));
+                    .Values(std::vector<float>(n, smargon->chi_deg)));
         add(DetectorTransformation("phi", TransformationType::Rotation, smargon->phi_axis)
-                    .Value(smargon->phi_deg));
+                    .Values(std::vector<float>(n, smargon->phi_deg)));
     }
 
     return chain;
diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 1b73a6d6..3ff34466 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -14,6 +14,7 @@ This is an UNSTABLE release. It includes many experimental features, as well as
 * Tests: a tilted detector is now cross-checked against pyFAI and DIALS, in the unit tests and against a written file in CI.
 * rugnux: the detector geometry is also logged in XDS's convention (`ORGX`/`ORGY`, detector axis vectors, rotation axis), so it can be compared directly with an XDS refinement.
 * HDF5: a data file missing next to a VDS master now reads as the error-pixel marker instead of zero counts, so those frames are masked rather than silently integrated as blank.
+* HDF5: a still or grid scan recorded with a Smargon head position is no longer read back as a single image.
 * The writer refuses a stream whose start message declares a different pixel format than its images carry, instead of writing a master that does not describe its own data.
 * HDF5: `module_offset` is written as a float with a proper unit vector, and every transformation offset declares `offset_units`, so a reader does not fall back to the axis's own units - degrees on a rotation - when interpreting a length.
 * The image stream can carry the sample transformation chain (`transformations`, in the END message) in mounting order, so a goniometer axis, the Smargon chi/phi and a grid stage are described together and unambiguously. It is optional - a producer that does not send it gets the same chain built by the writer - so no metadata version change is needed.
diff --git a/writer/HDF5NXmx.cpp b/writer/HDF5NXmx.cpp
index fef8391c..281e8e52 100644
--- a/writer/HDF5NXmx.cpp
+++ b/writer/HDF5NXmx.cpp
@@ -758,15 +758,22 @@ void NXmx::Sample(const StartMessage &start, const EndMessage &end) {
 
     // Smargon chi/phi are static positioners closest to the sample, so they are appended
     // at the innermost end of the transformation chain (whatever depends_on currently is).
-    auto write_smargon = [&start](HDF5Group& transformations, std::string& depends_on) {
+    auto write_smargon = [&start, &end](HDF5Group& transformations, std::string& depends_on) {
         if (!start.smargon_position)
             return;
-        SaveScalar(transformations, "chi", start.smargon_position->chi_deg)->
+
+        // One entry per image, even though neither angle moves. A reader takes the number of images
+        // from the innermost axis of the sample chain when no axis varies - chi and phi are innermost
+        // whenever they are present - so written as scalars, a still with a head position reads back
+        // as a single image however many were collected.
+        const auto n = static_cast<size_t>(std::max<int64_t>(end.max_image_number, 1));
+
+        SaveVector(transformations, "chi", std::vector<double>(n, start.smargon_position->chi_deg))->
                 Transformation("deg", depends_on, "", "", "rotation",
                     {start.smargon_position->chi_axis.x, start.smargon_position->chi_axis.y,
                      start.smargon_position->chi_axis.z}, {0, 0, 0}, "");
         depends_on = "/entry/sample/transformations/chi";
-        SaveScalar(transformations, "phi", start.smargon_position->phi_deg)->
+        SaveVector(transformations, "phi", std::vector<double>(n, start.smargon_position->phi_deg))->
                 Transformation("deg", depends_on, "", "", "rotation",
                     {start.smargon_position->phi_axis.x, start.smargon_position->phi_axis.y,
                      start.smargon_position->phi_axis.z}, {0, 0, 0}, "");