diff --git a/ext/zstds_ext/dictionary.c b/ext/zstds_ext/dictionary.c
index 9d8abe9..c069015 100644
--- a/ext/zstds_ext/dictionary.c
+++ b/ext/zstds_ext/dictionary.c
@@ -165,6 +165,8 @@ VALUE zstds_ext_get_dictionary_header_size(VALUE ZSTDS_EXT_UNUSED(self), VALUE b
 
 #else
   zstds_ext_raise_error(ZSTDS_EXT_ERROR_NOT_IMPLEMENTED);
+
+  return SIZET2NUM(0);
 #endif
 }