diff --git a/documentation/release_5.1.htm b/documentation/release_5.1.htm
index a6fe2ff93a..c84bf7ce5a 100644
--- a/documentation/release_5.1.htm
+++ b/documentation/release_5.1.htm
@@ -122,6 +122,10 @@ <h3>Changed functionality</h3>
   <li>(private) bitfields <code>random</code> or <code>isRandom</code> have been renamed to <code>delayed</code>
     to avoid confusion. Affected listmode file formats are SAFIR, ECAT962 and ECAT966.
   </li>
+  <li><code>DiscretisedDensityDensity::has_same_characteristics</code> now adds actual origins and grid spacing to the explanation if they are different.
+  </li>
+  <li><code>ProjMatrixByBinSPECTUB</code> prints an explanation when the attenuation image has different characteristics.
+  </li>
 </ul>
 
 <h3>Build system and dependencies</h3>
diff --git a/src/include/stir/DiscretisedDensity.inl b/src/include/stir/DiscretisedDensity.inl
index 2798d865c7..e4aa5646af 100644
--- a/src/include/stir/DiscretisedDensity.inl
+++ b/src/include/stir/DiscretisedDensity.inl
@@ -81,8 +81,16 @@ actual_has_same_characteristics(DiscretisedDensity<num_dimensions, elemT> const&
     }
 
   if (norm(other.get_origin() - this->get_origin()) > 1.E-2)
-    { 
-      explanation = "Not the same origin.";
+    {
+      char tmp[2000];
+      snprintf(tmp, 2000, "Not the same origin: (%g,%g,%g) and (%g,%g,%g)",
+	      other.get_origin()[1],
+	      other.get_origin()[2],
+	      other.get_origin()[3],
+	      this->get_origin()[1],
+	      this->get_origin()[2],
+	      this->get_origin()[3]);
+      explanation = tmp;
       return false;
     }
   if (other.get_index_range() != this->get_index_range())
diff --git a/src/include/stir/DiscretisedDensityOnCartesianGrid.inl b/src/include/stir/DiscretisedDensityOnCartesianGrid.inl
index 3acaa5d4ae..821676b7ee 100644
--- a/src/include/stir/DiscretisedDensityOnCartesianGrid.inl
+++ b/src/include/stir/DiscretisedDensityOnCartesianGrid.inl
@@ -92,13 +92,14 @@ actual_has_same_characteristics(DiscretisedDensity<num_dimensions, elemT> const&
   if (norm(other.get_grid_spacing() - this->get_grid_spacing()) > 1.E-4F*norm(this->get_grid_spacing()))
     {
       char tmp[2000];
-      sprintf(tmp, "Not the same grid spacing: (%g,%g,%g) and (%g,%g,%g)",
+      snprintf(tmp, 2000, "Not the same grid spacing: (%g,%g,%g) and (%g,%g,%g)",
 	      other.get_grid_spacing()[1],
 	      num_dimensions>1?other.get_grid_spacing()[2]:0.,
 	      num_dimensions>2?other.get_grid_spacing()[3]:0.,
 	      this->get_grid_spacing()[1],
 	      num_dimensions>1?this->get_grid_spacing()[2]:0.,
 	      num_dimensions>2?this->get_grid_spacing()[3]:0.);
+      explanation = tmp;
       return false;
     }
 
diff --git a/src/recon_buildblock/ProjMatrixByBinPinholeSPECTUB.cxx b/src/recon_buildblock/ProjMatrixByBinPinholeSPECTUB.cxx
index de65ca7c7c..411c195947 100644
--- a/src/recon_buildblock/ProjMatrixByBinPinholeSPECTUB.cxx
+++ b/src/recon_buildblock/ProjMatrixByBinPinholeSPECTUB.cxx
@@ -710,9 +710,9 @@ set_up(
 	if ( wmh.do_att ){
         if (is_null_ptr(attenuation_image_sptr))
             error("Attenuation image not set."); 
-
-        if (!density_info_ptr->has_same_characteristics(*attenuation_image_sptr))
-            error("Currently the attenuation map and emission image must have the same dimension, orientation, and voxel size.");
+        std::string explanation;
+        if (!density_info_ptr->has_same_characteristics(*attenuation_image_sptr, explanation))
+            error("Currently the attenuation map and emission image must have the same dimension, orientation, and voxel size:\n" + explanation);
 
         if ( ( attmap = new (nothrow) float [ wmh.vol.Nvox ] ) == nullptr )
             error("Error allocating space to store values for attenuation map.");
diff --git a/src/recon_buildblock/ProjMatrixByBinSPECTUB.cxx b/src/recon_buildblock/ProjMatrixByBinSPECTUB.cxx
index a7c293fcd9..c6ae155aa2 100644
--- a/src/recon_buildblock/ProjMatrixByBinSPECTUB.cxx
+++ b/src/recon_buildblock/ProjMatrixByBinSPECTUB.cxx
@@ -541,8 +541,9 @@ set_up(
 	if ( wmh.do_att || wmh.do_msk_att ){
                 if (is_null_ptr(attenuation_image_sptr))
                     error("Attenation image not set");
-		if (!density_info_ptr->has_same_characteristics(*attenuation_image_sptr))
-			error("Currently the attenuation map and emission image must have the same dimension, orientation and voxel size");
+                std::string explanation;
+		if (!density_info_ptr->has_same_characteristics(*attenuation_image_sptr, explanation))
+			error("Currently the attenuation map and emission image must have the same dimension, orientation and voxel size:\n" + explanation);
 
 		attmap = new float [ vol.Nvox ];
 		std::copy(attenuation_image_sptr->begin_all(), attenuation_image_sptr->end_all(),attmap);