--- a/liboctave/Array.cc
+++ b/liboctave/Array.cc
@@ -831,6 +831,41 @@
   return nc;
 }
 
+#if defind (_AIX)
+template <class T>
+T&
+DiagArray<T>::elem (int r, int c)
+{
+  static T foo (0);
+  return (r == c) ? Array<T>::elem (r) : foo;
+}
+
+template <class T>
+T&
+DiagArray<T>::checkelem (int r, int c)
+{
+  static T foo (0);
+  if (r < 0 || c < 0 || r >= nr || c >= nc)
+    {
+      (*current_liboctave_error_handler) ("range error");
+      return foo;
+    }
+  return (r == c) ? Array<T>::elem (r) : foo;
+}
+
+template <class T>
+T&
+DiagArray<T>::operator () (int r, int c)
+{
+  static T foo (0);
+  if (r < 0 || c < 0 || r >= nr || c >= nc)
+    {
+      (*current_liboctave_error_handler) ("range error");
+      return foo;
+    }
+  return (r == c) ? Array<T>::elem (r) : foo;
+}
+
 template <class T>
 T&
 DiagArray<T>::xelem (int r, int c)

--- a/liboctave/Array.h
+++ b/liboctave/Array.h
@@ -227,6 +227,7 @@
 template <class T>
 class DiagArray : public Array<T>
 {
+#if ! defined (_AIX)
 private:
 
   class Proxy
@@ -276,6 +277,7 @@
   };
 
 friend class Proxy;
+#endif
 
 protected:
 
@@ -303,6 +305,11 @@
   int cols (void) const;
   int columns (void) const;
 
+#if defined (_AIX)
+  T& elem (int r, int c);
+  T& checkelem (int r, int c);
+  T& operator () (int r, int c);
+#else
   Proxy elem (int r, int c)
   {
     return Proxy (this, r, c);
@@ -329,6 +336,7 @@
     else
       return Proxy (this, r, c);
   }
+#endif
 
 // No checking.
   T& xelem (int r, int c);

--- a/src/pt-const.cc
+++ b/src/pt-const.cc
@@ -611,7 +611,15 @@
 
   i++;
 
-  assert (i > 0 && (nr <= 1 || nc <= 1));
+  assert (i >= 0 && (nr <= 1 || nc <= 1));
+
+// This function never reduces the size of a vector, and all vectors
+// have dimensions of at least 0x0.  If i is 0, it is either because
+// a vector has been indexed with a vector of all zeros (in which case
+// the index vector is empty and nothing will happen) or a vector has
+// been indexed with 0 (an error which will be caught elsewhere).
+  if (i == 0)
+    return;
 
   if (nr <= 1 && nc <= 1 && i >= 1)
     {