diff --git a/src/system/runtime_loader/runtime_loader.c b/src/system/runtime_loader/runtime_loader.c
index 2ace6ec913..7a178e96c9 100644
--- a/src/system/runtime_loader/runtime_loader.c
+++ b/src/system/runtime_loader/runtime_loader.c
@@ -310,7 +310,7 @@ test_executable(const char *name, uid_t user, gid_t group, char *invoker)
 		// test for shell scripts
 		if (!strncmp(buffer, "#!", 2)) {
 			char *end;
-			buffer[length - 1] = '\0';
+			buffer[min_c((size_t)length, sizeof(buffer) - 1)] = '\0';
 
 			end = strchr(buffer, '\n');
 			if (end == NULL) {