diff --git a/common/DiffractionExperiment.cpp b/common/DiffractionExperiment.cpp
index 21068756..8ca90dc6 100644
--- a/common/DiffractionExperiment.cpp
+++ b/common/DiffractionExperiment.cpp
@@ -614,8 +614,11 @@ void DiffractionExperiment::CheckDataProcessingSettings(const SpotFindingSetting
     check_finite("Spot finding low resolution limit", settings.low_resolution_limit);
 
     // An unset high-resolution limit means "as far as the detector reaches", so there is nothing to check.
-    if (settings.high_resolution_limit.value_or(0.0f) > 0) {
+    // A value that is present still has to be finite - NaN fails every comparison below, so testing it
+    // inside the branch would let it through unchecked.
+    if (settings.high_resolution_limit.has_value())
         check_finite("Spot finding high resolution limit", *settings.high_resolution_limit);
+    if (settings.high_resolution_limit.value_or(0.0f) > 0) {
         check_min("Spot finding high resolution limit", *settings.high_resolution_limit, 0.5);
         check_max("Spot finding high resolution limit", *settings.high_resolution_limit, 50.0);
         if (settings.low_resolution_limit > 0) {
diff --git a/image_analysis/spot_finding/SpotUtils.cpp b/image_analysis/spot_finding/SpotUtils.cpp
index 638e0c7c..210cf595 100644
--- a/image_analysis/spot_finding/SpotUtils.cpp
+++ b/image_analysis/spot_finding/SpotUtils.cpp
@@ -147,8 +147,11 @@ void SpotAnalyze(const DiffractionExperiment &experiment,
 
     CountSpots(output, spots_out, spot_finding_settings.cutoff_spot_count_low_res);
 
+    // 0 spells "no limit" everywhere else the limit is read (value_or(0) then compares against it), so it
+    // has to mean the same here - passing it on as a resolution makes ResolutionShells throw per image.
+    const auto &spot_d_min = spot_finding_settings.high_resolution_limit;
     GenerateSpotPlot(output, spots_out,
-                     spot_finding_settings.high_resolution_limit.value_or(experiment.GetDetectorMaxResolution_A()));
+                     spot_d_min.value_or(0.0f) > 0 ? *spot_d_min : experiment.GetDetectorMaxResolution_A());
 
     output.resolution_estimate = GetResolution(spots_out);