diff --git a/include/cn-cbor/cn-cbor.h b/include/cn-cbor/cn-cbor.h
index 4dfb771..553aa55 100644
--- a/include/cn-cbor/cn-cbor.h
+++ b/include/cn-cbor/cn-cbor.h
@@ -362,7 +362,7 @@
  * @return                   True on success
  */
 bool cn_cbor_mapput_string(cn_cbor* cb_map,
-                           char* key, cn_cbor* cb_value
+                           const char* key, cn_cbor* cb_value
                            CBOR_CONTEXT,
                            cn_cbor_errback *errp);
 
diff --git a/src/cn-create.c b/src/cn-create.c
index 37e8f35..bc448e9 100644
--- a/src/cn-create.c
+++ b/src/cn-create.c
@@ -125,7 +125,7 @@
 }
 
 bool cn_cbor_mapput_string(cn_cbor* cb_map,
-                           char* key, cn_cbor* cb_value
+                           const char* key, cn_cbor* cb_value
                            CBOR_CONTEXT,
                            cn_cbor_errback *errp)
 {