--- a/src/defun-int.h
+++ b/src/defun-int.h
@@ -172,13 +172,21 @@
 
 // How mapper functions are actually installed.
 
+// XXX FIXME XXX -- Really want to avoid the following casts, since
+// (as always with casts) it may mask some real errors...
+
 #define DEFUN_MAPPER_INTERNAL(name, ch_map, d_b_map, c_b_map, d_d_map, \
 			      d_c_map, c_c_map, lo, hi, \
 			      can_ret_cmplx_for_real, doc) \
   install_builtin_mapper \
-    (new octave_mapper (ch_map, d_b_map, c_b_map, d_d_map, d_c_map, \
-			c_c_map, lo, hi, \
-			can_ret_cmplx_for_real, #name))
+    (new octave_mapper \
+     (X_CAST (octave_mapper::ch_mapper, ch_map), \
+      X_CAST (octave_mapper::d_b_mapper, d_b_map), \
+      X_CAST (octave_mapper::c_b_mapper, c_b_map), \
+      X_CAST (octave_mapper::d_d_mapper, d_d_map), \
+      X_CAST (octave_mapper::d_c_mapper, d_c_map), \
+      X_CAST (octave_mapper::c_c_mapper, c_c_map), \
+      lo, hi, can_ret_cmplx_for_real, #name))
 
 #endif /* ! MAKE_BUILTINS */