diff --git a/include/asterisk/stringfields.h b/include/asterisk/stringfields.h
index d35ef7d8ec..c3d6759437 100644
--- a/include/asterisk/stringfields.h
+++ b/include/asterisk/stringfields.h
@@ -235,7 +235,7 @@ void __ast_string_field_index_build_va(struct ast_string_field_mgr *mgr,
 */
 #define ast_string_field_index_set(x, index, data) do { \
     char *__zz__ = (char*)(x)->__begin_field[index]; \
-    int __dlen__ = strlen(data); \
+    size_t __dlen__ = strlen(data); \
     if( __dlen__ == 0 ) { (x)->__begin_field[index] = __ast_string_field_empty; \
     } else { \
      if( __zz__[0] != 0 && __dlen__ <= strlen(__zz__) ) { \
@@ -250,7 +250,7 @@ void __ast_string_field_index_build_va(struct ast_string_field_mgr *mgr,
 #ifdef FOR_TEST
 #define ast_string_field_index_logset(x, index, data, logstr) do { \
     char *__zz__ = (char*)(x)->__begin_field[index]; \
-    int __dlen__ = strlen(data); \
+    size_t __dlen__ = strlen(data); \
     if( __dlen__ == 0 ) { (x)->__begin_field[index] = __ast_string_field_empty; \
     } else { \
      if( __zz__[0] != 0 && __dlen__ <= strlen(__zz__) ) { \