diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 4f2b51e6e..17b5c07d8 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -2,6 +2,7 @@
 ## 1.0.0
 ### 1.0.0-rc.166
 * `rugnux` reads a PILATUS miniCBF rotation sweep natively, with no conversion: naming any frame - or the directory holding it - processes the whole sweep that frame's template belongs to. `--mode scale` still needs a `_process.h5`.
+* A master whose companion `_meta.h5` was not kept still opens: the fields an Eiger master links into that file are treated as absent rather than as a read error, and a run that finds no saturation value anywhere says so and carries on instead of refusing the dataset.
 * `jfjoch_viewer` opens PILATUS miniCBF sweeps - naming any frame opens the whole sweep - and can run a processing job on one.
 * A miniCBF sweep takes its rotation axis from the goniometer angles the header states, instead of assuming the axis every such file was previously assumed to have.
 * A miniCBF sweep takes the mounting from the imgCIF axis table its header carries - which laboratory direction the image's columns and rows run along, and which the spindle turns about - and, where there is no table, from a `+SLOW` on the `Oscillation_axis` line, which says the spindle runs along the image's slow direction.
diff --git a/reader/HDF5MetadataSource.cpp b/reader/HDF5MetadataSource.cpp
index 20bef0df3..65a0bbeb6 100644
--- a/reader/HDF5MetadataSource.cpp
+++ b/reader/HDF5MetadataSource.cpp
@@ -986,10 +986,26 @@ HDF5MetadataSource::OpenResult HDF5MetadataSource::Open(const std::string &filen
                 ReadLength_m(*master_file, "/entry/instrument/detector/sensor_thickness") * 1e6);
         if (master_file->Exists("/entry/instrument/detector/sensor_material"))
             detector.SensorMaterial(master_file->GetString("/entry/instrument/detector/sensor_material"));
-        detector.SaturationLimit(SaturationLimitFromValue(
-                ReadIntWithLegacyFallback(*master_file,
-                        "/entry/instrument/detector/saturation_value",
-                        "/entry/instrument/detector/detectorSpecific/countrate_correction_count_cutoff")));
+        // Optional, because a file that states no saturation value anywhere is a real and common
+        // thing: an Eiger master links saturation_value into a companion _meta.h5, and a deposited
+        // dataset frequently does not include that file, leaving neither the NXmx name nor the
+        // DECTRIS one readable. Left unset, DiffractionExperiment::GetSaturationLimit() falls back
+        // to the container's own overflow, which is the safe direction - it can only fail to call a
+        // pixel saturated, where too LOW a value drops the whole reflection and silently removes the
+        // strongest data (see BitDepthImage below). Refusing the file outright is the one option that
+        // helps nobody.
+        if (master_file->Exists("/entry/instrument/detector/saturation_value")
+            || master_file->Exists("/entry/instrument/detector/detectorSpecific/countrate_correction_count_cutoff"))
+            detector.SaturationLimit(SaturationLimitFromValue(
+                    ReadIntWithLegacyFallback(*master_file,
+                            "/entry/instrument/detector/saturation_value",
+                            "/entry/instrument/detector/detectorSpecific/countrate_correction_count_cutoff")));
+        else
+            Logger("HDF5Reader").Warning("The file states no saturation value - neither NXmx saturation_value nor "
+                           "the DECTRIS countrate_correction_count_cutoff is readable, which is what "
+                           "an Eiger master looks like when its companion _meta.h5 was not kept. No "
+                           "pixel will be called saturated; if this detector overloads, its strongest "
+                           "reflections will be integrated as if they were valid.");
         // The reader hands every image out as signed int32 whatever the file stored (see PixelSigned
         // below), so that is the container depth the rest of the code has to see. DetectorSetup defaults
         // DECTRIS to 16 bits and GetByteDepthImage() prefers the detector's value over the image
diff --git a/tests/HDF5WritingTest.cpp b/tests/HDF5WritingTest.cpp
index 535e13e55..99a0f9b1a 100644
--- a/tests/HDF5WritingTest.cpp
+++ b/tests/HDF5WritingTest.cpp
@@ -1451,3 +1451,34 @@ TEST_CASE("HDF5FilePusher_finalize_failure_recovers", "[HDF5FilePusher][Repro]")
             std::filesystem::remove(e.path());
     REQUIRE(H5Fget_obj_count(H5F_OBJ_ALL, H5F_OBJ_ALL) == 0);
 }
+
+// A link that is written in the file and points at something not there is NOT an existing dataset.
+// Every DECTRIS Eiger master links saturation_value, pixel_mask, bit_depth_readout and
+// serial_number into a companion <prefix>_meta.h5, and that file is routinely not kept when a
+// dataset is archived or deposited. Asking only whether the LINK exists then answers yes and the
+// read that follows throws, which turns every optional-field guard in the reader into a hard
+// failure - measured on a deposited Eiger 16M set that could not be opened at all.
+TEST_CASE("HDF5Objects_dangling_external_link_does_not_exist", "[HDF5][Unit]") {
+    const std::string fname = "test_dangling_link.h5";
+    remove(fname.c_str());
+    {
+        HDF5File file(fname);
+        HDF5Group group(file, "/entry");
+        group.SaveScalar("present", static_cast<int64_t>(7));
+        // ...and a link into a file that does not exist, exactly as an orphaned Eiger master has.
+        REQUIRE(H5Lcreate_external("no_such_meta.h5", "/_dectris/whatever",
+                                   group.GetID(), "absent", H5P_DEFAULT, H5P_DEFAULT) >= 0);
+    }
+    {
+        HDF5ReadOnlyFile file(fname);
+        CHECK(file.Exists("/entry/present"));
+        CHECK(file.GetInt("/entry/present") == 7);
+        // The link is there, the object is not.
+        CHECK(H5Lexists(file.GetID(), "/entry/absent", H5P_DEFAULT) > 0);
+        CHECK_FALSE(file.Exists("/entry/absent"));
+        // ...so an optional read of it falls back instead of throwing.
+        CHECK(file.GetString("/entry/absent", "fallback") == "fallback");
+    }
+    remove(fname.c_str());
+    REQUIRE(H5Fget_obj_count(H5F_OBJ_ALL, H5F_OBJ_ALL) == 0);
+}
diff --git a/writer/HDF5Objects.cpp b/writer/HDF5Objects.cpp
index 9f951476f..5f3ef778f 100644
--- a/writer/HDF5Objects.cpp
+++ b/writer/HDF5Objects.cpp
@@ -1072,7 +1072,16 @@ std::string HDF5Object::GetString(const std::string &name, const std::string &de
 
 bool HDF5Object::Exists(const std::string &name) const {
     H5E_BEGIN_TRY {
-        return H5Lexists(GetID(), name.c_str(), H5P_DEFAULT) > 0;
+        // The LINK has to be there and the object it names has to be reachable. Those are two
+        // different questions for an external link, and every DECTRIS Eiger master asks the second
+        // one: it links saturation_value, pixel_mask, bit_depth_readout and serial_number into a
+        // companion <prefix>_meta.h5 that is routinely not kept when a dataset is archived or
+        // deposited. H5Lexists then says yes - the link is written in the master - and the read that
+        // follows throws, which turns every optional-field guard in the reader into a hard failure
+        // and refuses the whole file over a value it was prepared to do without.
+        if (H5Lexists(GetID(), name.c_str(), H5P_DEFAULT) <= 0)
+            return false;
+        return H5Oexists_by_name(GetID(), name.c_str(), H5P_DEFAULT) > 0;
     } H5E_END_TRY;
     return false;
 }