diff --git a/src/sources/source.h b/src/sources/source.h
index bc65dbc..125bfe7 100644
--- a/src/sources/source.h
+++ b/src/sources/source.h
@@ -5,6 +5,7 @@
  * published by the Free Software Foundation.
  */
 #include <assert.h>
+#include <errno.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>