diff --git a/src/AtomMask.cpp b/src/AtomMask.cpp
index 6e6512a359..497200a551 100644
--- a/src/AtomMask.cpp
+++ b/src/AtomMask.cpp
@@ -196,8 +196,16 @@ void AtomMask::AddAtomRange(int minAtom, int maxAtom) {
 
 /** Add atoms in given unit to mask. */
 void AtomMask::AddUnit(Unit const& unitIn) {
+  // Atoms in a unit should already be sorted, and should have no duplicates.
   for (Unit::const_iterator it = unitIn.segBegin(); it != unitIn.segEnd(); ++it)
-    AddAtomRange( it->Begin(), it->End() );
+  {
+    //AddAtomRange( it->Begin(), it->End() );
+    for (int atom = it->Begin(); atom < it->End(); atom++)
+      Selected_.push_back( atom );
+  }
+  // Update Natom_ if necessary
+  if (Selected_.back() >= Natom_)
+    Natom_ = Selected_.back() + 1;
 }
 
 // AtomMask::AddMaskAtPosition()
diff --git a/src/Version.h b/src/Version.h
index b85eef9ba4..c9554bb47b 100644
--- a/src/Version.h
+++ b/src/Version.h
@@ -12,7 +12,7 @@
  * Whenever a number that precedes <revision> is incremented, all subsequent
  * numbers should be reset to 0.
  */
-#define CPPTRAJ_INTERNAL_VERSION "V6.29.15"
+#define CPPTRAJ_INTERNAL_VERSION "V6.29.16"
 /// PYTRAJ relies on this
 #define CPPTRAJ_VERSION_STRING CPPTRAJ_INTERNAL_VERSION
 #endif