diff --git a/src/buffer.c b/src/buffer.c
index 8e892da..ee962b2 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -5522,7 +5522,12 @@
 		current_sctx.sc_seq = 0;
 		current_sctx.sc_lnum = 0;
 #endif
+		// Make sure no risky things are executed as a side effect.
+		++sandbox;
+
 		retval = do_set(s, OPT_MODELINE | OPT_LOCAL | flags);
+
+		--sandbox;
 #ifdef FEAT_EVAL
 		current_sctx = save_current_sctx;
 #endif