diff --git a/src/api/api_model.cpp b/src/api/api_model.cpp
index 63092b2cf..10ede0922 100644
--- a/src/api/api_model.cpp
+++ b/src/api/api_model.cpp
@@ -50,14 +50,13 @@ extern "C" {
         Z3_CATCH;
     }
 
-    Z3_ast Z3_API Z3_model_get_const_interp(Z3_context c, Z3_model m, Z3_func_decl a) {
+    Z3_ast_opt Z3_API Z3_model_get_const_interp(Z3_context c, Z3_model m, Z3_func_decl a) {
         Z3_TRY;
         LOG_Z3_model_get_const_interp(c, m, a);
         RESET_ERROR_CODE();
         CHECK_NON_NULL(m, 0);
         expr * r = to_model_ref(m)->get_const_interp(to_func_decl(a));
         if (!r) {
-            SET_ERROR_CODE(Z3_INVALID_ARG);
             RETURN_Z3(0);
         }
         mk_c(c)->save_ast_trail(r);
diff --git a/src/api/c++/z3++.h b/src/api/c++/z3++.h
index 6e8544770..9fb664819 100644
--- a/src/api/c++/z3++.h
+++ b/src/api/c++/z3++.h
@@ -1582,6 +1582,9 @@ namespace z3 {
 	    return static_cast<unsigned>(i) < num_consts() ? get_const_decl(i) : get_func_decl(i - num_consts());
 	}
 
+        // returns interpretation of constant declaration c.
+        // If c is not assigned any value in the model it returns 
+        // an expression with a null ast reference.
         expr get_const_interp(func_decl c) const {
             check_context(*this, c);
             Z3_ast r = Z3_model_get_const_interp(ctx(), m_model, c);
diff --git a/src/api/python/z3.py b/src/api/python/z3.py
index 848883ba3..2126cf0fe 100644
--- a/src/api/python/z3.py
+++ b/src/api/python/z3.py
@@ -5516,7 +5516,10 @@ class ModelRef(Z3PPObject):
             decl = decl.decl()
         try:
             if decl.arity() == 0:
-                r = _to_expr_ref(Z3_model_get_const_interp(self.ctx.ref(), self.model, decl.ast), self.ctx)
+                _r = Z3_model_get_const_interp(self.ctx.ref(), self.model, decl.ast)
+                if _r.value is None:
+                    return None
+                r = _to_expr_ref(_r, self.ctx)
                 if is_as_array(r):
                     return self.get_interp(get_as_array_func(r))
                 else: