diff --git a/pvDataApp/misc/sharedVector.h b/pvDataApp/misc/sharedVector.h
index 755e256..cd8ee39 100644
--- a/pvDataApp/misc/sharedVector.h
+++ b/pvDataApp/misc/sharedVector.h
@@ -47,13 +47,18 @@ namespace detail {
         template<typename E1> friend class shared_vector_base;
     protected:
         std::tr1::shared_ptr<E> m_data;
-        //! Offset in the data array of first element
+        //! Offset in the data array of first visible element
         size_t m_offset;
         //! Number of visible elements between m_offset and end of data
         size_t m_count;
         //! Total number of elements between m_offset and the end of data
         size_t m_total;
 
+        /* invariants
+         *  m_count <= m_total (enforced)
+         *  m_offset + m_total <= (size_t)-1 (checked w/ assert())
+         */
+
     public:
 
         //! @brief Empty vector (not very interesting)
@@ -68,6 +73,9 @@ namespace detail {
         {
             if(!m_data.get()) {
                 m_offset = m_total = m_count = 0;
+            } else {
+                // ensure we won't have integer overflows later
+                assert( m_offset <= ((size_t)-1) - m_total);
             }
         }
     public:
@@ -96,6 +104,8 @@ namespace detail {
     protected:
         typedef typename meta::strip_const<E>::type _E_non_const;
     public:
+        //! Constructor used to implement freeze().
+        //! Should not be called directly.
         shared_vector_base(shared_vector_base<_E_non_const>& O,
                            _shared_vector_freeze_tag)
             :m_data()
@@ -109,6 +119,8 @@ namespace detail {
             O.clear();
         }
 
+        //! Constructor used to implement thaw().
+        //! Should not be called directly.
         shared_vector_base(shared_vector<const E>& O,
                            _shared_vector_thaw_tag)
             :m_data()
@@ -180,20 +192,16 @@ namespace detail {
          */
         void slice(size_t offset, size_t length=(size_t)-1)
         {
-            if(offset>m_total)
-                offset = m_total;
+            if(offset>m_count)
+                offset = m_count; // will slice down to zero length
+
+            const size_t max_count = m_count - offset;
 
             m_offset += offset;
 
             m_total -= offset;
 
-            if(offset>m_count) {
-                m_count = 0;
-            } else {
-                if(length > m_count - offset)
-                    length = m_count - offset;
-                m_count = length;
-            }
+            m_count = std::min(length, max_count);
         }
 
         // Access to members.
diff --git a/testApp/misc/testSharedVector.cpp b/testApp/misc/testSharedVector.cpp
index a1bcd1f..0c1487d 100644
--- a/testApp/misc/testSharedVector.cpp
+++ b/testApp/misc/testSharedVector.cpp
@@ -250,7 +250,13 @@ static void testSlice()
     testOk1(half2.dataOffset()==5);
     testOk1(half2a.dataOffset()==5);
 
-    testOk1(half2.size() == half2a.size());
+    testOk1(half1.size()==5);
+    testOk1(half2.size()==5);
+    testOk1(half2a.size()==5);
+
+    testOk1(half1.dataTotal()==10);
+    testOk1(half2.dataTotal()==5);
+    testOk1(half2a.dataTotal()==5);
 
     testOk1(original.data() == half1.data());
     testOk1(half2.data() == half2a.data());
@@ -259,13 +265,17 @@ static void testSlice()
     half2.slice(1);
     half2a.slice(1,1);
 
+    testOk1(half1.dataOffset()==5);
+    testOk1(half2.dataOffset()==6);
+    testOk1(half2a.dataOffset()==6);
+
     testOk1(half1.size()==0);
     testOk1(half2.size()==4);
     testOk1(half2a.size()==1);
 
-    testOk1(half1.dataOffset()==10);
-    testOk1(half2.dataOffset()==6);
-    testOk1(half2a.dataOffset()==6);
+    testOk1(half1.dataTotal()==5);
+    testOk1(half2.dataTotal()==4);
+    testOk1(half2a.dataTotal()==4);
 
     half2.clear();
     testOk1(half2.dataOffset()==0);
@@ -525,7 +535,7 @@ static void testICE()
 
 MAIN(testSharedVector)
 {
-    testPlan(154);
+    testPlan(162);
     testDiag("Tests for shared_vector");
 
     testDiag("sizeof(shared_vector<int>)=%lu",