diff --git a/include/wx/arrstr.h b/include/wx/arrstr.h
index bed1098d74..951dd16d1b 100644
--- a/include/wx/arrstr.h
+++ b/include/wx/arrstr.h
@@ -398,8 +398,10 @@ private:
   // (if the old buffer is big enough, just return NULL).
   wxString *Grow(size_t nIncrement);
 
-  // Binary search in the sorted array
-  size_t BinarySearch(const wxString& str, bool equal = false) const;
+  // Binary search in the sorted array: return the index of the string if it's
+  // present, otherwise, if lowerBound is true, return the position at which
+  // the string should be inserted and if it's false return wxNOT_FOUND.
+  size_t BinarySearch(const wxString& str, bool lowerBound) const;
 
   size_t  m_nSize,    // current size of the array
           m_nCount;   // current number of elements
diff --git a/src/common/arrstr.cpp b/src/common/arrstr.cpp
index 3611bc4276..65317bb1e8 100644
--- a/src/common/arrstr.cpp
+++ b/src/common/arrstr.cpp
@@ -379,7 +379,7 @@ void wxArrayString::Shrink()
 }
 
 // Binary search in the sorted array
-size_t wxArrayString::BinarySearch(const wxString& str, bool equal) const
+size_t wxArrayString::BinarySearch(const wxString& str, bool lowerBound) const
 {
     size_t
         lo = 0,
@@ -398,7 +398,7 @@ size_t wxArrayString::BinarySearch(const wxString& str, bool equal) const
             return i;
     }
     wxASSERT_MSG(lo == hi, wxT("binary search broken"));
-    return equal ? wxNOT_FOUND : lo;
+    return lowerBound ? lo : wxNOT_FOUND;
 }
 
 // searches the array for an item (forward or backwards)
@@ -408,7 +408,7 @@ int wxArrayString::Index(const wxString& str, bool bCase, bool bFromEnd) const
     // use binary search in the sorted array
     wxASSERT_MSG( bCase && !bFromEnd,
                   wxT("search parameters ignored for auto sorted array") );
-    return BinarySearch(str, true);
+    return BinarySearch(str, false /* not lower bound */);
   }
   else {
     // use linear search in unsorted array
@@ -438,7 +438,7 @@ size_t wxArrayString::Add(const wxString& str, size_t nInsert)
 {
   if ( m_autoSort ) {
     // insert the string at the correct position to keep the array sorted
-    size_t nIndex = BinarySearch(str);
+    size_t nIndex = BinarySearch(str, true /* return lower bound */);
     Insert(str, nIndex, nInsert);
     return nIndex;
   }