retain constness of maps
diff --git a/libasn1compiler/asn1c_C.c b/libasn1compiler/asn1c_C.c
index 16f7f3c..d8f60c3 100644
--- a/libasn1compiler/asn1c_C.c
+++ b/libasn1compiler/asn1c_C.c
@@ -730,7 +730,7 @@
 			tag2el_cxer_count);
 		OUT("%d,\t/* Whether extensible */\n",
 			compute_extensions_start(expr) == -1 ? 0 : 1);
-		OUT("(unsigned int *)asn_MAP_%s_mmap_%d\t/* Mandatory elements map */\n",
+		OUT("(const unsigned int *)asn_MAP_%s_mmap_%d\t/* Mandatory elements map */\n",
 			p, expr->_type_unique_index);
 	);
 	OUT("};\n");