diff --git a/sub-process.c b/sub-process.c
index fcc4832c14..ec9a51b7b1 100644
--- a/sub-process.c
+++ b/sub-process.c
@@ -181,8 +181,8 @@ static int handshake_capabilities(struct child_process *process,
 			if (supported_capabilities)
 				*supported_capabilities |= capabilities[i].flag;
 		} else {
-			warning("subprocess '%s' requested unsupported capability '%s'",
-				process->argv[0], p);
+			die("subprocess '%s' requested unsupported capability '%s'",
+			    process->argv[0], p);
 		}
 	}