diff --git a/core/AmArg.cpp b/core/AmArg.cpp
index 549d0122..4e713ff2 100644
--- a/core/AmArg.cpp
+++ b/core/AmArg.cpp
@@ -87,7 +87,7 @@ void AmArg::push(const AmArg& a) {
   v_array->push_back(a);
 }
 
-const size_t AmArg::size() {
+const size_t AmArg::size() const {
   assertArray();  
   return v_array->size(); 
 }
diff --git a/core/AmArg.h b/core/AmArg.h
index 4695287e..afc9cdc3 100644
--- a/core/AmArg.h
+++ b/core/AmArg.h
@@ -134,7 +134,7 @@ class AmArg
   // operations on arrays
   void push(const AmArg& a);
   
-  const size_t size();
+  const size_t size() const;
 
   /** throws OutOfBoundsException if array too small */
   AmArg& get(size_t idx);